Go ahead and move to another carrier if all you care about is getting a buggy phone that resets constantly. I used to work for the first carrier to have that treo 650 and its almost as buggy and messed up as the original 600. From what I've heard they haven't fixed the bugs for Verizon or cingular either. I'm waiting for a less buggy version myself. If T-mobile did release the treo 650 in the shape its in now everyone would cry that they wasted their money on a bad product and that its T-mobiles fault, etc....
I heard it daily while working for the other carrier from the same people that complained about the 600 then purchased the 650 as soon as it came out. Also with edge rolling out I will be waiting for an edge enabled device also!

Just get an unlocked 650. I have one and works great with T-Mobile. When you put in your sim, It automatically gets the setting for T-Mobile internet and VPN, so if you have the the data plan with TMO, You will be able to use it. It is an awesome phone but it does reset for me from time to time...