Right. You are only on a network at a given time. However, 3G allows data and voice usage at the same time; you only have access to one or the other on EDGE.
I have the same "straight to VM" issues with the iphone. It happens a lot, and gets quite embarassing when my supervisor calls me to tell me where and when to report to work, and it goes straight to voicemail even though I am sitting right next to the phone and didn't hear it ring, It drives me crazy.
The only time I've had any major issue with my phone was in Vegas this past FF. I'd done an upgrade on it that morning and later in the evening I couldn't make or receive calls or texts. After 3 hours, friends started worrying cuz I'd headed back the room alone. I restarted my phone and got a FLOOD of texts and vm's from the previous 3 hours.
That's about it. I think I've been pretty lucky with my phone or service or whichever it is. It only drops calls in the same spot on my commute. Sometimes I'll receive a text more than once, but that's usually something on the sender's end. When I lived at my old pad, my phone would be working fine, while my 2 friends on the couch next to me had no service on their iphones. I hear about all these issues and I think "wft? I've never had that happen"
great, I probably just jinxed myself...