one thing to consider in all this is that with GSM/GPRS/EDGE you cant do data and voice at the same time. get a voice call while the data stream is ongoing, if your lucky it will cut the data stream and go to call, if your unlucky the caller will be passed to voicemail or get a busy signal. thats the thing about UMTS/HSPA, it can do data while doing voice (thats basically what a video call is doing), so one can for instance look up a phone number if its a unknown caller. hell, maybe have the system refuse the call if the number is on a database of known sales numbers...