Ask HN: Best VoIP service to replace cell carrier?

I am looking to drop my cell service provider and exclusively use a VoIP app or service instead. Some considerations:

* Cheap

* Can port my current number.

* Prefer not running my own server for this

* Can receive calls through phone (or app) if connected to wifi.

Constant conmectivity is not important, only that I receive vmail & texts when I connect. I dont really care much about vmail. I plan to get a calyx router when I can afford it which will provide wifi continuously. I have os x and an iphone.