Looking through the GV features, I think I'm interested in trying it out in the "use my existing phone number" version. I'm curious how it works, though. I mean, at an under-the-hood level, if I'm not changing my phone number, how is it that it can do things like intercept my voicemail messages and change the greeting for different callers?

If I sign up for this, will I lose my Visual Voicemail on the iPhone?