T-Mobile doesn't charge the subsidized plan price if you don't buy a subsidized phone from them. Or at least they didn't as recently as a year ago. I pay $60/month instead of $80 because I bought my Nexus One from Google.
"Today, there are over a million T-Mobile customers using unlocked iPhones on our network," [T-Mobile USA Chief Marketing Office Cole] Brodman continued. "We are interested in offering all of our customers a no-compromise iPhone experience on our network."
