Not that it really matters, but just to clarify; T-Mobile is not owned by Vodafone. T-Mobile is a huge-ass german company. Vodafone owns Verizon.
For the original poster - like everyone said it cannot be done. If you think youll look that much cooler with an iphone, then you need to switch to ATT (save yourself the headache of bricken it while trying to get it on T-Mobile.
And the new Touch Diamond should be hitting Verizon soon enough. I'd get this insteed. http://www.htc.com/www/product.aspx?id=46280