I'm looking to replace my N4 because it broke. I bought it from Google and started the $30 plan on tmobile. Since I kinda don't want to drop another $30th now, can someone explain the $50/$60/$70 plans, specifically are you locked in after you pay off the phone? I know it's a month to month thing, but once I pay off the phone (if I pay it off early), must I stay with tmobile and move around only those plans? Can I ever switch back to the $30 plan? I ask because I work offshore, so the $30 plan works best for me. I am dropping money on a new apartment now, though, hence the interest in buying from tmobile instead of Google and paying off later. Thoughts?