I want to buy the New Smartphone, the Sony Ericsson Xperia x10.  I'm on the T-Mobile USA network.  Is there anything I should know?  I'd also heard rumors that T-Mobile USA might offer this phones, so maybe buying it through them is cheaper than buying the an unlocked thru retail sites.  but I'm not too sure.  
I want this phone as soon as possible, and I believe it'll work in USA and on the T-Mobile network.  I could've buy it this moment, but if the rumors are true, I can save quite a bit by buying thru T-Mobile.  If it's not, then I won't have to wait and be disappointed.  
Also, I was asked to buy the Vivaz for my sis and Vivaz pro for another, both also on T-Mobile USA network.  
Anything, problems, issues I should know about these?