referring more particularly to the drawing by characters of reference , fig1 - 4 illustrate a touch tone type telephone 10 comprising the usual and well known transmitter and receiver of electrical impulses and converter of such impulses into audio sounds . since telephone 10 is well known , it will not be described further except to note that the telephone has an electrical circuit interconnecting a source of power to the touch tone button type plungers 11 mounted on the face 12 of housing 13 of the telephone which can be interrupted by one or more on - off switches , if so desired , to control the transmission of electrical pulses from the telephone to a central station for transmission to other like telephones . although the telephone 10 does not have a hand set shown , such part of the telephone would be used and placed in the cradle 14 of housing 13 in a well known manner . the push - buttons 15 , 15 &# 39 ; when depressed by the hand set ( not shown ) position the telephone circuits in a condition for receiving incoming calls . in their upward positions shown , which they assume when the receiver is out of the cradle , they condition the circuits in the telephone for transmitting outwardly of the telephone and complete circuits for receiving and transmitting impulses convertible to audio sounds . in order to provide selective accessory connection with a given telephone as well as to prevent an unauthorized caller from calling out from a given touch tone telephone 10 , a new clip - on lock and switching device 16 is interconnected with telephone 10 at the existing cradle 14 formed in the telephone housing 13 , as shown in fig1 and 2 of the drawing . the clip - on electronic lock and switching device comprises a housing 18 formed of a suitable plastic or like moldable material which at least partially encloses the electronic lock and selector switching device and employs suitable logic for accomplishing the locking or switching functions disclosed . as shown in fig2 a selector switching card 19 employing the logic for the various switching functions hereinafter explained comprises a flat card shown also in fig3 which is mounted in the base of the housing between pairs of cooperating ridges 20 and 21 at opposite ends of housing 18 . housing 18 comprises a shell - like hollow configuration having a ridged end 22 projecting upwardly from a relatively flat top surface 23 . the ridged end 22 is conformed to fit between and complete the shape of projections 24 forming a part of cradle 14 . at the end of surface 23 of housing 18 opposite to its ridged end 22 , the housing is provided with a clip configuration 25 . this clip configuration comprises a leg member 26 forming a part of the extended surface 27 of end 28 of housing 18 which is reverse bent to extend juxtapositioned to and spaced from the bottom surface of switching card 19 in the manner shown in fig2 and 6 . the leg member 26 of clip configuration 25 is provided with a distortion or groove 29 extending across at least a part of the width of clip configuration 25 and partially surrounds and interlocks with a bend or protrusion 31 formed on a ledge 32 . ledge 32 projects into a cavity 17 that is formed below the cradle 14 at the housing 13 of telephone 10 . thus , the clip configuration of housing 18 can be moved longitudinally into cavity 17 of housing 13 so as to detachably connect housing 18 to housing 13 in such an arrangement that the surface 27 of housing 18 forms substantially an extension of the outer surface or contour of projection 24 of housing 13 . as shown in fig2 the bottom of switching card 19 is mounted flush to the bottom of the cradle for the telephone and is kept in place by spring tension created by the memory of the plastic material from which housing 18 and particularly leg member 26 are formed . it should be noted that housing 18 of the clip - on device 16 is intended to provide a plurality of discrete functions depending on the electronic gear and logic mounted on the switching card 19 or modifications thereof . as shown in fig6 housing 18 &# 39 ; of the clip - on device 16 &# 39 ; is modified to receive a logic bearing card 19 &# 39 ; through a slot 33 formed in the ridged end 22 &# 39 ; of the housing . this card is intended to guard the telephone against unauthorized use and makes and breaks an electric circuit in a well known manner by its movement into and out of slot 33 . a pair of lead wires , not shown in fig6 connect the plungers 11 to the telephone circuitry through a circuit on the switch card 19 &# 39 ; when the card is in the slot 33 of housing 18 &# 39 ; and is broken when the card is removed from slot 33 in housing 18 &# 39 ;. it should be noted when the clip - on device of fig6 is utilized , card 19 , shown in fig2 does not comprise a part of the structure . with regard to card 19 and its function in housing 18 , this card may provide the discrete function of enabling the receiver of a call on a single line telephone to place the caller &# 34 ; on hold &# 34 ; and to switch the caller onto an extension of this single line telephone . to operate the telephone to accomplish this option , the called party having the clip - on device installed on his telephone merely depresses a light emitting diode ( led ) push - button switch 34 &# 39 ; as he hangs up his telephone handset . this push - button switch 34 or 34 &# 39 ; illuminates to indicate that the holding circuit is engaged and will extinguish when any extension is picked up . fig5 is a cross - sectional view of one of the push - button led switches 34 , 34 &# 39 ; shown in fig1 and 3 . each switch comprises a plunger 41 &# 39 ; employing a pair of juxtapositioned rods serving as conductors 35 , only one of which being shown . conductor rods 35 are spring biased with the plunger 41 &# 39 ; to the circuit open position shown in the drawing against an internal ledge 37 of its housing 38 by a pair of coil springs 36 , only one of which being shown . a pair of contacts 39 and 40 are interconnected by a bridging member forming a part of plunger 41 &# 39 ; when plunger 41 &# 39 ; is depressed against the bias of spring 36 , only one of which being shown . dome 42 &# 39 ; of the led switch is illuminated when plunger 41 &# 39 ; is depressed and its bridging member makes contact with contacts 39 and 40 . coil springs 36 serve as conductors for interconnecting conductors 35 and 41 &# 34 ; of each of the led switches 34 , 34 &# 39 ; in the manner shown in fig4 . fig4 illustrates that the network system of the telephone is connected to the telephone company &# 39 ; s circuit ( not shown ) through lines 41 and 42 , respectively . a double throw toggle switch 43 connected to the network system connects the network to either line 1 or line 2 depending on the line selected by the user of the telephone set through circuits 44 and 45 , respectively . it should be noted that the logic shown for the lines 1 and 2 are identical but they could be different if so desired . the second hold line is connectable to either an outside line or an inside intercom line through a second two position toggle switch 46 or to connect both outside lines to the called telephone . the remaining logic for line 2 comprises similar logic components as in line 1 including the push - button switch 34 &# 39 ;. an optional 3 . 5 mm jack 47 is installed in the rear of the clip on device 16 , as shown in fig1 and 4 , for providing a means for connecting through cable 48 a radio or cassette player ( not shown ) into the clip - on device for providing music to the caller when he or she is temporarily placed &# 34 ; on hold &# 34 ;. although the logic for accomplishing the various switching functions of the clip - on device 16 are well known functions , it is believed to be novel to accomplish these discrete functions by the disclosed simple but efficient clip - on device which fits into the cradle of a telephone and requires a minimum of changes or interruptions to the normal telephone &# 39 ; s connection to the telephone network . when the clip - on device is modified , as shown in fig6 the card 19 &# 39 ; merely comprises a switching function to either complete the telephone network connection to the telephone circuits when the card is inserted in the housing 18 &# 39 ; or to interrupt the circuitry when the card is removed from slot 33 in housing 18 &# 39 ;. although but a few embodiments of the present invention have been illustrated and described , it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims .