the basic idea of the disclosure is that : by converging the non ims network and the voip network , a user of the non ims network may initiate , through the non ims network , a service to another user subscribing a convergence service , which may be implemented by the voip network , so as to facilitate the user to select the service access network and reduce the charge of the user &# 39 ; s call . the voip network of the disclosure may be an ims network , an ngn , a soft switching network or the like , to implement the convergence of the call to a non ims network ( a gsm network and a cdma network ). in the disclosure , users may decide , according to a strategy , when to preferentially use voip , or when to initiate and reply a call use the non ims network . furthermore , the aforementioned strategy and mechanisms such as a forking call , a serial call or call forwarding on no reply may be implemented by the control over convergence call . when a user is able to access a wlan or in a roaming area of high charge ( such as international roaming ), the user may preferentially use the voip to initiate or reply a call . moreover , by the control of convergence call , the user may call another user of a non ims network by the non ims network number of the user , or another user of the non ims network may call the user by the non ims network number of the user . the user has a user identifier of ims voip ( sip uri or tel uri ) and a non ims network number ( such as a telephone number of gsm or cdma ), and two numbers are bound together by the control of convergence call . the user being abroad may use the voip of ims to initiate a call . if the call is to a local user of the non ims network , the ims routs the call to the non ims network , and sets the calling number to the non ims network number of the caller , where the call is charged in accordance with a local call or a low charge . if other users of non ims network call the non ims network number of the user , the call control may be converged to transfer the call from the non ims network to the ims network ( for example , registering the call forwarding service with the non ims network , or being triggered by an intelligent network and change the number to the ims ), and to transmit the call to the voip terminal of the user by the ims . in the disclosure , because of the charge , the management strategy or other reasons , it is necessary to limit the use of the convergence call or part of functions of the convergence call of some users from some areas ( geographic locations ). thus , it is required to have a process of certification to the registration of the convergence call or to the request of certain applications of the convergence call , and the registration and the application request which do not meet the requirement may be refused . for example , for a user being allowed to use the convergence call during the international roaming but not in the country , the convergence call initiated by the user in the country will be registered to the ims unsuccessfully . alternatively , in the case that a user is allowed to use the convergence call during the international roaming , and is allowed to use an instance message ( im ) service in the country rather than the call service of the convergence call , the user is not allowed to call in the country , but may register the im . in regard to the process of certification , the geographic location information or the extended network element which bears the geographic location information in an existing message ( such as registration , call and message ) may be determined according to existing registration procedure . furthermore , in consideration of security , a registration request message may be encrypted to prevent the forgery of the user . fig1 shows a flowchart of convergence call according to an embodiment of the disclosure . according to fig1 , the flow of the convergence call in the example includes : step 1 : other users initiate a call in a non ims network , wherein the callee in the call request is the non ims network number of a convergence call user . step 2 : a non ims network forwards the call request to a call session control function entity ( cscf ) of a voip network ( such as an ims , an ngn , or a soft switching network ) by a non ims network interworking device . wherein , when the non ims network is a cs network and the voip network is an ims , the non ims network interworking device is an mgcf or an ip multimedia media gateway ( im - mgw ). when the non ims network is a soft switching network and the voip network is an ims , the non ims network interworking device may be a soft switching device . the non ims network interworking device packages the call request of the non ims network by an sip message , and sends the packaged call request to the cscf . step 3 : the cscf sends a call to the convergence call as . step 4 : the convergence call as performs the call according to the principle of voip terminal precedence or non ims network terminal precedence based on the convergence call control strategy stored by the convergence call as . the call is performed according to the principle of voip terminal precedence in the example . step 7 : the convergence call as calls the non ims network terminal when the branch of precedence call has no reply or is busy . in the step , in the process of calling the non ims network terminal , the non ims network interworking device is needed to be used . the forwarding the call to the voip network by the non ims network may be implemented by the following ways : subscribing a forwarding service to the non ims network number of the convergence call user , for example , a forwarding number subscribing an ims number ( in format of tel ), which is a cs domain roaming number ( csrn ) in the non ims network and is converted into an ims domain roaming number ( imrn ) by a media gateway controller function entity ( mgcf ); or subscribing change number triggering to the non ims network number of the convergence call user , triggering to the intelligent network scf and executing the change number operation , wherein the scf is an independent device ; or subscribing change number triggering to the non ims network number of the convergence call user , triggering to the intelligent network scf and executing the change number operation , wherein the scf and the convergence call as are set together . fig2 shows another flowchart of convergence call according to an embodiment of the disclosure . according to fig2 , the procedure of convergence call in the example includes : step 1 : other users initiate a call in a non ims network , wherein the callee in the call request is the non ims network number of a convergence call user . step 2 : a non ims network forwards the call request to a call session control function entity ( cscf ) of a voip network ( such as an ims , an ngn , or a soft switching network ). wherein , when the non ims network is a cs network and the voip network is an ims , the non ims network interworking device is an mgcf or an ip multimedia media gateway ( im - mgw ). when the non ims network is a soft switching network and the voip network is an ims , the non ims network interworking device may be a soft switching device . the non ims network interworking device packages the call request of the non ims network by an sip message , and sends the packaged call request to the cscf . step 3 : the cscf sends the call request to the convergence call as . step 4 : the convergence call as performs a forking call on the voip terminal and the non ims network terminal according to its own strategy . step 5 : when one of the voip terminal and the non ims network terminal replies , for example , the voip terminal replies , 200ok is sent to the convergence call as . step 6 : the convergence call as sends 200ok to the caller , and releases the other call branch ( such as the non ims network in the figure ). fig3 shows a flowchart of certification of registration according to an embodiment of the disclosure . according to fig3 , the flow of certification of registration in the example includes : step 1 : a voip terminal ( such as an ims terminal of an ims network ) initiates registration to a cscf ( sending a registration request message to the cscf ), wherein the registration request message includes the current address information of the voip terminal . step 2 : the cscf decides , according to the strategy stored by the cscf and the current address on which the voip terminal is located , whether to accept the registration request . step 3 : a failure response is sent to the voip terminal if the registration request is refused . it should be noted that the current address information of the voip terminal may be included either in a connection address cell in the registration request message or in a specified extension field . the address information may be encrypted . the strategy may be : the registration requests initiated from certain addresses ( or according to the geographical location information corresponding to the address information ) should be refused . of course , the strategy may also be : the voip terminal in a set location area can only reply but not call . in the disclosure , the setting of the strategy is not limited , and the strategy may be set according to the requirements of operators . fig4 shows a flowchart of certification of registration according to an embodiment of the disclosure . according to fig4 , the flow of certification of registration in the example includes : step 1 : a voip terminal ( such as an ims terminal of an ims network ) initiates registration to a cscf ( i . e ., sending a registration request message to the cscf ), wherein the registration request message includes the address information of the voip terminal . step 2 : the cscf sends a registration request message to a convergence call as , wherein the registration request message includes the current address information of the voip terminal . step 3 : the convergence call as decides , according to the strategy stored by the cscf and the current address on which the voip terminal is located , whether to accept the registration request . step 4 : the convergence call as sends a failure response to the cscf if the registration request is refused . step 5 : the cscf sends a failure response to the voip terminal . it should be noted that the strategy may be : the registration requests initiated from certain addresses ( or according to the geographical location information corresponding to the address information ) should be refused . of course , the strategy may also be : the voip terminal in a set location area can only reply but not call . in the disclosure , the setting of the strategy is not limited , and the strategy may be set according to the requirements of operators . fig5 shows a flowchart of verification of application according to an embodiment of the disclosure . according to fig5 , the flow of verification of an application includes : step 1 : a voip terminal ( such as an ims terminal of an ims network ) initiates an application to a cscf ( i . e ., sending an application request message to the cscf ), wherein the application request message includes the current address information of the voip terminal . step 2 : the cscf sends an application request message to a convergence call as , wherein the application request message includes the current address information of the voip terminal . step 3 : the convergence call as decides , according to the strategy stored by the cscf and the current address on which the voip terminal is located , whether to accept the application request . step 4 : the convergence call as sends a failure response to the cscf if the registration request is refused . step 5 : the cscf sends a failure response to the voip terminal . the strategy may be : the registration requests initiated from certain addresses ( or according to the geographical location information corresponding to the address information ) should be refused . of course , the strategy may also be : the voip terminal in a set location area can only reply but not call . in the disclosure , the setting of the strategy is not limited , and the strategy may be set according to the requirements of operators . fig6 shows a flowchart of calling of a moving user by unified access code according to an embodiment of the disclosure . according to fig6 , the flow of calling by a moving user using a unified access code includes : step 1 : other users initiate a call in a non ims network , wherein the callee of the call is the non ims network number of a convergence call user . step 2 : a non ims network forwards the call to a cscf of a voip network ( such as an ims , an ngn , or a soft switching network ) by a non ims network interworking device . wherein , when the non ims network is a cs network and the voip network is an ims , the non ims network interworking device is an mgcf or an m - mgw . when the non ims network is a soft switching network and the voip network is an ims , the non ims network interworking device may be a soft switching device . when the voip network is not able to provide enough csrn numbers , csrn is provided to each convergence call user as a forwarding number . here , the forwarding number may be a unified access code . the access code corresponds to the psi of the convergence call as . step 4 : after receiving the call request , the convergence call as may correspondingly converge the voip number and the non ims network number of the convergence call user according to the original called number . step 5 : the subsequent convergence call procedures are the same as the procedures shown in fig1 and fig2 , which are not repeated here . the disclosure further provides a system for converging a call , which applies to a network where a non ims network and a voip network are converged . the non ims network interworking device is set in the non ims network , and the non ims network is converged with the voip network by the non ims network interworking device . the non ims network is configured to , when the non ims network determines that a callee receiving a call request is a convergence call user , forward the call request to the voip network ; and when the non ims network is a cs domain network and the voip network is an ims , the non ims network interworking device is an mgcf and / or an im - mgw ; or when the non ims is a soft switching network and the voip network is an ims , the non ims network interworking device is a soft switching device . the non ims network is also configured to : convert a forwarding number of the callee into the roaming number of the voip network according to a forwarding service subscribed with a non ims network number of the callee , and forward the call request to the voip network according to the roaming number of the voip network . alternatively , the non ims network is further configured to trigger the call request to an scf of an intelligent network according to a change number triggering service subscribed with a non ims network number of the callee , wherein the call request is forwarded to the voip network by the scf . the non ims network is further configured to send the call request to an cscf of the voip network ; the cscf is further configured to send the call request to an as ; and the as is further configured to initiate the call to the callee according to a call convergence strategy . calling the voip terminal preferentially , and forwarding the call to a non ims network terminal of the callee when the voip terminal is busy or has no reply ; or calling the voip terminal and the non ims network terminal of the callee at the same time , and releasing one of the voip terminal and the non ims network terminal after receiving a reply from the other of the voip terminal and the non ims network terminal . the voip terminal initiates a registration request to the cscf , wherein the registration request comprises an address on which the voip terminal is located ; and the cscf determines whether the address on which the voip terminal is located is an address allowing the voip terminal to be registered ; when the address on which the voip terminal is located is the address allowing the voip terminal to be registered , the cscf allows the voip terminal to register ; and when the address on which the voip terminal is located is not the address allowing the voip terminal to be registered , the cscf refuses the voip terminal to register . the cscf forwards the registration request to the as , wherein the registration request comprises an address on which the voip terminal is located ; and the as determines whether the address on which the voip terminal is located is an address allowing the voip terminal to be registered ; when the address on which the voip terminal is located is the address allowing the voip terminal to be registered , the as allows the voip terminal to register ; and when the address on which the voip terminal is located is not the address allowing the voip terminal to be registered , the as refuses the voip terminal to register . the cscf forwards the application request to the as , wherein the application request comprises an address on which the voip terminal is located ; and the as determines whether the address on which the voip terminal is located is an address allowing the voip terminal to be registered ; when the address on which the voip terminal is located is the address allowing the voip terminal to be registered , the as allows the voip terminal to register ; and when the address on which the voip terminal is located is not the address allowing the voip terminal to be registered , the as refuses the voip terminal to register . the above are only the preferable embodiments of the disclosure , but are not intended to limit the scope of protection of the claims of the disclosure . in the embodiments of the disclosure , by converging the non ims network and the voip network , a user of the non ims network may initiate , through the non ims network , a service to another user subscribing a convergence service , which may be implemented by the voip network , so as to facilitate the user to select the service access network and reduce the charge of the user &# 39 ; s call .