Serious question (because I don't know the answer): do any of those services allow you to make/receive calls at your computer, via your mobile phone line?
I dont think so. I believe they use VOIP. But when/if I make calls from my laptop using the google chat web browser plug-in they go out and it has my caller ID on it.
Is it a big positive to have the calls originate from your cellular connection? I think the industry is moving away from cellular calls and moving towards using VOIP over data to save money on Cellular plans with fewer minutes.