I switched to Simple Mobile back in November (T-Mobile MVNO) and couldn't be happier. $50 for all-you-can-eat talk, text, domestic and international text and 4G speeds.
I am considering the same $30 T-Mobile pre-paid plan you're about to get into and simply porting my cell number to Google Voice. I just don't want my number permanently parked with Google in case I change my mind later on.
Anybody know if Google keeps your number forever or can you port it away from Google if you want?