If you own the iPhone and do some cool stuff with it, get Google Voice.
With Google Voice, you can read voicemail like a text message, receive incoming calls to your home to ring your cellphone, desk phone or even office phone.
It means, when your friend calls ONE number, all of your phones ring (you can set setting, of course).
The best part about it is free — it’s by Google, you know?
The only catch is you’d have to be invited. Yes, it’s by invitation only. Google loves doing that to you.
Here is the link, send your email and wait for the invitation — https://www.google.com/voice