fig1 illustrates an sms distribution path according to the invention . in the prior art , the short messages have usually been directed to a single subscriber or a specified group of subscribers such as a sales team . however , gsm also supports a feature known as cell broadcast in which messages can be sent to all the subscribers in a particular area . in the embodiment of the invention illustrated , a message consists of the telephone number of an advertiser and an alphanumeric tag to identify the advertiser . an operator enters the message into a terminal 1 . the message is then coded into a secure format known to applicants as an embedded command stream ( ecs ) and sent via a modem 2 and a fixed line 3 to a local gsm switch 4 . according to its delivery address , the message is delivered to any or all of the other switches within that network , or even across networks . the switch 4 , which in this example is in the geographical area to which the message is to be transmitted , delivers the message to a number of cellsites 5 . the cellsites 5 are the base transceiver stations of the gsm network . each cellsite 5 then broadcasts the message to a group of transceivers or mobile telephones , hereinafter referred to as “ mobiles ”. if cell broadcast is used , the group consists of all mobiles within the geographical area at the time of the broadcast . a selected mobile 6 receiving the message transmits a confirmation of receipt back to its respective cellsite 5 . from now on , until an update situation , the system will not contact this mobile 6 again . the mobile 6 recognizes the message as sms data and passes it to a sim card 7 , which is a small self - contained microprocessor , held in a slot in the mobile 6 . the sim card 7 in turn recognizes the ecs using special hardware and software and stores the message in memory in such a way that it may not be overwritten by the subscriber . known sim cards contain a large number of fixed memory locations in which the subscriber can store frequently dialed numbers and corresponding alphanumeric tags . the sim card 7 of the invention stores the message in one of these locations , and then carries out a write protect operation . the locations dedicated to storing write protected messages may be designated by code numbers relating to a particular category of advertiser . thus , for example , car hire company telephone numbers can be stored in location 01 , hotel reservations in location 02 and so on . fig2 shows a call placing process in which a subscriber communicates with an advertiser . the subscriber , remembering that the car hire company &# 39 ; s number is in location 01 as shown at 8 , keys in a short code corresponding to the location , such as 01 #. the mobile 6 then interrogates the sim card 7 to retrieve the telephone number from the location . the sim card 7 provides both the number and the alphanumeric tag giving the company &# 39 ; s name and displays it to the subscriber . the user confirms that he wishes to proceed by pressing send . next , the mobile obtains a voice channel through which the call proceeds to the dialed number . the gsm system automatically handles intra - network and inter - network hops . at this point the subscriber can hold a voice conversation with the company . providing the correct equipment has been installed at the company , as soon as the call is answered , subscriber identity information read from the sim card 7 gives the company immediate customer billing details such as a name and address . the sim card 7 also contains information detailing the subscriber &# 39 ; s credit account . this information is held in a separate , secure memory location , accessible only when the subscriber enters a mandatory pin number , known only to himself , thus confirming that the mobile has not been stolen or lost . when the subscriber has confirmed his car hire deal , he enters the pin number into the mobile 6 , requesting the credit information from the sim card 7 . the sim card 7 supplies the information and the mobile uses existing voice / data techniques to transmit the information to the company , in a format secure against detection by fraudsters . the sale is confirmed by the company or its equipment and the call is terminated . in this example , it is also possible to obtain a telephone or fax number from the operator - assisted directory enquiries system without the subscriber having to manually enter the number into the communications terminal which he desires to use . to use this feature , the subscriber calls network directory enquiries and gives the name of the person , company or service of which he wishes to ascertain the telephone number , as well as any additional information requested by the operator answering the call . the operator then locates the number , confirms it and enquires as to whether the number is to be transmitted verbally , transferred over sms into a given memory location of the subscriber &# 39 ; s sim card or both . if the subscriber chooses a sim update , the voice call is terminated and the operator initiates the sms process by entering a sequence into a computer or pressing a dedicated button . the telephone number is then encoded into an ecs message at the dispatch center and is posted across the network to the subscriber &# 39 ; s communications terminal , which transmits a confirmation to the dispatch center . thus , the retry mechanism , which operates until such a confirmation is received , is suspended . the communications terminal recognizes the message as sms data , passes it to the sim card , and if capable , displays a “ message received ” banner . the sim card in turn recognizes the ecs using special hardware and software , and decodes it accordingly . the number , and any associated alphanumeric tag , which would normally consist of the name of the person or company , are recovered together with the memory location in which they are intended to be stored . the number and name - tag are then written to that location and are write - protected if requested by the subscriber , the overwrite protection being encoded into the message at source . subsequently , the subscriber attempts to place a call to the number in the known memory location by keying in the memory location number . the sim card passes the telephone or fax number to the communications terminal on demand , and upon receipt of the subscriber &# 39 ; s confirmation , the communications terminal sets up the call to the desired number . fig3 shows the electronic structure of the sim card 7 . the card communicates with the mobile to which it is connected via an input / output ( i / o ) manager 15 , preferably using the protocol iso 7816 t = 0 . a filter 16 receives incoming data from the i / o manager and detects any ecs messages from among the short messages received . the ecs messages are sent directly to an extended erasable read only memory ( e 2 rom ) 17 , which is preferably a “ flash ” e 2 rom . data can also be output from the e 2 rom directly to the i / o manager 15 . the remaining blocks shown in fig3 are standard components of a sim card . fig4 shows how the e 2 rom is organized . a root directory 18 contains a sim administration and identifier 19 , a gsm directory and network data 20 , and a telecom directory 21 . the telecom directory in turn contains memory locations as follows : “ abbreviated dial numbers ” 22 , “ capability configuration ” 23 , “ short messages ” 24 , “ fixed dial numbers ” 25 , and “ charging counter ” 26 . each block represents a plurality of memory locations . the frequently dialed numbers and corresponding alphanumeric tags are stored at locations 22 . the “ abbreviated dial numbers ” locations 22 and the “ short messages ” locations 24 each have an associated locking control file 27 , 28 , respectively . the locking control files constitute means for read / write protecting and removing read / write protection from their associated memory locations . the locking control files 27 , 28 will typically be in the telecom directory 21 as shown , however they can be located elsewhere such as in an administration directory . fig5 is a flowchart illustrating the operation of the sim card 7 , which uses the specially fabricated hardware and software which has been described above to implement the operations illustrated . at lozenge 9 , messages , requests , and instructions having ecs are distinguished from those without . each of these ecs types consists of a data stream headed by a command which is one of at least four types : write commands for the messages , read commands for the requests for information , attribute commands for lock or unlock instructions and run commands for instructions to run a program . the command and data types are decoded at box 10 and acted on in one of the four paths 11 - 14 . path 11 handles the write commands to store messages starting at a location specified therein . path 12 handles the read commands ; again , the requests for information contain a location to be accessed first . successive locations are read and the data stored in a buffer until the required amount of data has been read . the data in the buffer is then encoded into the ecs format and dispatched from the mobile using sms to the calling party . in path 13 , attribute commands are used to lock or unlock specified memory locations and render them accessible or inaccessible , either to calling parties or to the subscriber . in path 14 , run commands cause a program stored in the sim card to be run . the basic ecs system is expandable to up to 255 internal shell commands of which write , read , lock / unlock and run are four examples . the specific protocol used for the transfer of information is not fixed and could be iso7816 t = 0 or any other suitable protocol . the internal shell commands are a supplement to the ability of the system to create external file objects within the sim card 7 . the file objects are of two types : application data file programs ( adfp &# 39 ; s ) containing functional data which can be executed by the sim card processor and can self modify if required and application data files ( adf &# 39 ; s ) containing non - functional data which does not have these capabilities . existing adf ( p )&# 39 ; s can be modified over - the - air enabling advanced facilities such as personalization , re - personalization or downloadable phone book . the sim card 7 has a directory structure , similar to that of a computer disk , and new adf ( p )&# 39 ; s can be downloaded into any directory over the air . also over the air , directories can be created , deleted and modified , multiple tree directory operations can be carried out and adf ( p )&# 39 ; s that are no longer required can be deleted . the amount of adf ( p ) data which can be downloaded is limited only by the size of the e 2 rom memory of the card . the invention , as described , greatly extends the applications of sim cards . for example , using the value added services directory , subscribers can book hotels and airline seats over their mobiles quickly and easily . an additional advantage of this feature of the invention is that the geographical distribution of messages to cards in a specific area such as the south of france is facilitated . thus advertisers can direct their messages to all mobile subscribers in the specific area . this , is particularly useful when subscribers “ roam ” from one area to another and have no knowledge of local services . the directory enquiries download enables contact telephone or fax numbers to be delivered to a subscriber &# 39 ; s communications terminal without any intervention by the subscriber . the process of manually entering a number whilst engaged in a call to the operator is often dangerous , especially when the subscriber is driving . the ability of the system to download adf ( p )&# 39 ; s means that additional services can be added to the sim card over the air while maintaining total compatibility with the existing cellular system . thus the sim card could acquire the functions of a credit card , passport , driving license , car park pass , membership card and so on , becoming a multi - service card . also , dynamically updatable services can be added which require a different process to be run each time a service is accessed . once the card has extra services on it , it can be used outside of the mobile phone environment if desired as a standalone item . this can be read from or written to by a dedicated piece of hardware , such as a point of sale machine . if desired , the new services can be deleted , however the card will never lose its mobile phone sim capability . in addition , if the card has extra services , they will continue to function even if the subscriber has been disconnected from the mobile phone network , unless otherwise desired . modifications are possible without departing from the scope of the invention . for example , the sim card can be trained only to receive messages detailing services relevant to the subscriber &# 39 ; s needs .