I too have this problem. I can also state definitively that this is not a network-side error.

My wife and I live in MA, USA and use the AT&T mobile network. We have used the N95-1 (no US 3G), N82 (no US 3G), N97 (3.5G), and 5800xm (3.5G) from this location in the past 1 month.

All of these phones are capable of receiving calls while connected (or in processing of connecting) to the AT&T APN wap.cingular (note: this APN is used for all IP communications, despite it erferring to WAP and also it retaining hte name of the network at&t bought a few years back, it is the current and applicable full-network connectivity APN I always use, and even supports IPSEC VPN tunneling).

The N900 however is not capable of receiving calls while connected to this APN. Every incoming call is sent directly to voicemail. This appears to be distinctly a device-side fault and I am quite confused by other people reporting that they do not have this symptom.

Moreover, there has been at least one report in this forum appearing to claim that simultaneous voice and data was possible on a 2G network - not just that the data connection was dropped or suspended properly, but that simultaneous voice and data was possible. This, to the best of my understanding, is technically impossible and leads me to believe that we are not all testing for this problem in the same, reproducible and accurate, manner.

So, to the OP, I feel your pain. I have essentially disabled my packet data entirely, because though I hardly use my phone(s) for voice calls I know that it frustrates the crap out of my family when they try to call me and it goes persistently straight to voicemail.