The big innovation I've wanted to see for the longest time is missed call connecting. When AT&T drops my calls (which happens all the time), I call the person back and they call me back. We get each other's voicemails. Just connect the damn calls if we're calling each other.
I have set up a system with the people I talk to frequently. The person who initiated the call originally is the one responsible for calling back if there was a connection problem. Done.
I feel like a lot of these suggestions would rely heavily either on the existing networks (and we know how fast AT&T is at implementing things…), or would require Apple to invest a considerable amount of time and money into building the infrastructure behind these features.