Yeah I didn't think you could do this on CDMA phones, one of the main differences between them and GSM. GSM allows you to have an Internet and Phone connection at the same time. The most I have been able to do is send Texts while on the phone, but these don't utilize the Internet connection. anything else should be impossible really. I could be wrong though, but that's my understanding at least...
Update: I think the link Konfuzion posted is close, but think it really just disconnects data while on a call, which confused me b/c i thought that already happens automatically? My brain is fried so who knows, but I can tell you that I like your icon Konfuzion!