A 
system and method of simultaneously conducting a data transfer and a voice call between a 
mobile station and a radio 
telecommunications network having a mobile switching center (MSC) which serves the 
mobile station. A first embodiment includes a landline digital 
simultaneous voice and data (DSVD) modem associated with the 
mobile station which generates DSVD source 
signal and line negotiation protocols. The DSVD source 
signal and line negotiation protocols are encapsulated into circuit mode 
Radio Link Protocol (RLP) signals and transmitted to the MSC. An interworking function (IWF) associated with the MSC translates the circuit mode RLP signals into signals in a landline 
telecommunications protocol. In another embodiment, the voice call is carried 
over the air interface from the mobile 
station to the network in one timeslot, and the data transfer is carried in at least one additional timeslot on the same voice channel. In other embodiments, two voice channels may be allocated to the same mobile 
station. The voice call to a first party is carried from the mobile 
station to the 
network on one voice channel, and the data transfer to the first or a second party is carried on the second voice channel. The MSC hands off the two voice channels together, but releases them individually when either the voice call or the data transfer is completed.