LOUNE, it might be cheaper than that, depending on when you got your last phone. I’m with T-Mobile, and we’d had our phones forever. We upgraded and switched to the MyTouch 3G (the HTC G2 phone, really) and they just charged us an upgrade fee. I think it was $150 per phone, which is different from the $179 you mentioned above. During the upgrade, we were able to keep our old plan (which has more minutes for less than any plan they offer now) while simply adding on the data plan I needed for the Android OS. (My husband previously had a Blackberry and its data plan; they switched that over to the non-BB data plan for him.)
It was all pretty painless, and I love my MyTouch - Android’s a great OS. Definitely go into a store and have them talk over your options - they make it much clearer than what you can find out yourself on their website.