I have a Samsung Galaxy Mini I bought jailbroken off of Ebay for about 100 dollars. I use a pay-as-you-go card for calls and free wifi for the internet -- except for the part where I don't dare login to anything because anyone could probably root it on a whim, it's pretty awesome.
T-mobile. Payments through their website are a bit broken though, currently the only way I can put more minutes on is to use the refill cards, they don't seem to be able to accept my debit card.
Yes please, where? I'd really like to get some cheap-as-chips android phone to play with, as I've started doing android development. The Nexus 4 looks like it isn't happening, and honestly it wouldn't be healthy for me to have 24/7 web access. But a crappy little Chinese handset sounds perfect.