Thats's the difference between 3G and 2G..
with 3G you can do both.. but with GPRS it's one or the other
it depends on the Class of GPRS operation.
Can be connected to GPRS service and GSM service (voice, SMS), using both at the same time. Such devices are known to be available today.
Can be connected to GPRS service and GSM service (voice, SMS), but using only one or the other at a given time. During GSM service (voice call or SMS), GPRS service is suspended, and then resumed automatically after the GSM service (voice call or SMS) has concluded. Most GPRS mobile devices are Class B.
Are connected to either GPRS service or GSM service (voice, SMS). Must be switched manually between one or the other service.
this is clipped straight from the Wikipedia article on GPRS but it saves me writing it out in my own words!! Lathough having stated all this, my Nokia6230i is a pain the arse for not passing calls when on a BT/GPRS modem session to the laptop.
its also the main reason i want the bug fixed in the Vox that means it suddenly brings up a GPRS session for no apparent reason - i'm not sure if i've been missing calls!