I just tried to order a nexus one from google as an existing T-Mobile customer and found that I was only seeing a $US150 subsidy discount. I called T-Mobile and they indicated that I should see the full discount. They patched me through to HTC who then said I will only see the $US150 as existing T-Mobile customer and that is the agreement. Looks like some lines are crossed or Google/HTC are holding existing customers hostage. Needless to say, I’ll wait around and see if this changes.
Update: According to the pricing FAQ on the Nexus One, $US379 is the price for existing customers who are updating their data plans, $US279 is the price for existing customers adding data plans and the $US180 price seems to be reserved only for new T-Mobile customers. That’s some crap right there.