phone? What would I have to do in order to change phones if I say, bought a different, cheaper phone on ebay? Does it also have to be an android phone?
Your question is kind of confusing. If you have a G1, you can use it with any T-Mobile plan. If you want to switch plans, just call them and switch. They don't charge you anything differently for using a G1. I'm not sure what you're asking.