Thinking about moving from AT&T to the unlimited $30 T-Mobile plan

I purchased my Galaxy Nexus from the Google Play store so I can move freely to another carrier, however I want to keep my number (I've had it for nearly a decade!).

Has anyone here had success porting their number to Google Voice? If I do that and I'm on T-Mobile's unlimited plan I should be golden, right? I believe there is an option in Android to use Google Voice as your primary number when making calls and text. Please let me know if that's wrong.

Also, let me know what your set up is on other (cheaper) plans. I see some people saying their on T-Mobile with Skype out, others are using straight talk (first time I'm hearing about them). Any input would be helpful.

Thank you in advance!