For those confused on why data + voice works or doesn't work see:

http://en.wikipedia.org/wiki/General..._Radio_Service

look at the device classes.

SOME (e.g. very few devices) support Class A, but most EDGE/GPRS devices support Class B. Meaning either drop the data connection or drop the voice ability during data. Would have been nice if Apple gives a choice.

For UMTS/3G networks by default they can do both at the same time. e.g. my Nokia E61i when using T-Mobile in the US will suspend the data connection when a voice call comes in. In Germany on a UMTS network it will continue the data connection during a voice call.