I actually upgraded my phone through T-Mobile about a month ago, and it was a mistake. I went with the Free upgrade (mistake number one) and chose the Samsung SGH-T619.
It's a piece of crap. I guess I should have known that when I chose the free upgrade.
My biggest complaint: it won't send text messages. That's right, one of the core features of any mobile phone, and this lousy hunk of plastic won't do it. Every time I try to send a message, the phone says it couldn't do it, retry?
So I send an email to the customer service at T-Mobile. Complete form letter reply.
I'm going to throw this lousy phone in a drawer, and likely pay the penalty to switch to Cingular/ATT Mobile.
I am finally fed up.