So then on Verizon you could do everything but hit 'Send' on the email.
I too don't put much value on the simultaneous voice/data feature, but then again I have 2 phones, so I usually multitask by using two devices. Even without that though, I've never really felt a huge demand for the voice+data thing.
It's extremely useful when tethered. I find that I tether for hours at a time and I'm happy to be able to make/receive phone calls.
You could even hit 'Send'. The email would go out automatically at the next opportunity.
I'm not saying that simultaneous voice/data isn't useful. I'm saying that decent network coverage is more useful.
Edit: I also use Google Maps while talking, or check for movie times while someone is on the phone.