How much would it cost me if I want to upgrade to the iPhone 5?

I'm currently a T-Mobile customer and have another 1 year and 2 months left on my contract. I know that is a huge amount of time. I wanted to know how i could get the iPhone 5.could i ask t-mobile the upgrade cost, or could i buy the iphone 5 handset upfront (rrp) and sell my current iphone 4s. Then use the sim in the new iphone.

could this be done?

I'm in the same position with the full monty deal but I want to go from lumia 800 to lumia 920 when its out, get the lumia 920 it beats the iPhone 5 in every way and spec

You'd have to get the iPhone 5 from some other carrier like AT&T, then you'd have to wait for a method to unlock it to come out, and the phone without a contract could run for $650 plus tax and stuff. And no, you can't use your micro sim card with the iPhone 5 because the 5 has Nano Sim cards now, and I'm not even sure if T Mobile even has those. But if you want to sell your 4S for a high price and get the 5, you can take that risk.

Tmobile doesn't have the iphone.
you would need to buy an unlocked att iphone $799 then get a nano sim from tmobile.

I would suggest You see if Apples free iPhone 5 "test it keep it" promo offer is still available in your location. You simply give feedback on their product and keep the (phone) once you've given you opinion.

The technology giant has so far only confirmed the US prices, which are similar to the cost of the iPhone 4S when it was launched.
http://www.thisismoney.co.uk/money/bills/article-2202555/iPhone-5-prices-How-cost-recycle-old-phone-pay-less.html

Only $849.