Apps like Google Voice where I can port my phone number to text from my Android

Tablet? I'm looking for a service-that's free, where I can port my existing cell phone number to the app so I can text from my Nexus 7 as well as my phone, that way, if I don't have too, I can just take my Nexus 7 to places instead of my phone and my Nexus, yes I do realize I need an active internet connection for it to work Can you guys help me out? I don't want to pay $20 for the porting on Google Voice