You cannot page a MS in a data session, unless :
1. the phone is able to listen to the PCH while in transfer mode
2. the Gs interface (MSC – SGSN) is implemented
3. your BSS is able to coordinate the CS Paging towards MS in transfer mode.
For 3G, there is no such problem because data and voice are handled by the same network. In 2G, the voice is handled by MSC, the data by SGSN.