I got an iPhone 4 which I bought unlocked from timtechs and using it with T-mobile as well but on Pay as you go. But as far as I know you can keep existing TMO plan with unlocked phone.

I am currently looking to purchase a smartphone that can run on t-mobile service. I am looking at the myTouch 4g and Samsung Galaxy S phones. These phones are very expensive to just buy the phone itself, however the myTouch 4g and Galaxy S both get huge discounts with a 2 year service plan. From what I understand If I upgrade my phone to one of these, I will be forced into paying an extra 10$ a month for the data plan? Personally, the data plan is useless for me because 90% of the time I am within a wifi enables building which I should be able to latch onto with these phones (given I am permitted onto the wifi networks)? Because I do not want to pay extra for the data plan I will might dish out the $ to buy the phone itself (from bestbuy or online). If I do so will I be able to run my current plan on my the phone or will I be forced to activate it or something like that in which t-mobile will refuse service unless I add the data plan??

Any help is greatly appreciated!!!!