I don't understand what so many of you are complaining about. If the pricing changes, t-mobile customers won't have to pay any more than another what, $5-$10/month more than what you are paying now. In the short-term at&t customers will benefit from T-mobile's HSPA+ network and in the future, T-mobile customers will benefit from at&t's LTE network. And everyone will benefit from the larger coverage area resulting in fewer dropped calls and better overall coverage. Complaints that at&t has worse customer service may be legit, but who cares, you only need to deal with them once every two years unless you break your phone.
Concerning the inevitable loss of unlimited data to t-mobile customers, in my opinion, unlimited data is a thing of the past and t-mobile was bound to get rid of it eventually anyway. Sprint may be sticking with it for now but they aren't going to be able to keep that up if more people start tethering for free with jailbroken iphones or rooted androids. Best thing a person could do right now is immediately get a 2 year contract with sprint or t-mobile to lock in their unlimited data for 2 years because I highly doubt that plan option will be available by the time the contract ends.
The only negative thing I could see coming out of this is possibly the less innovation idea. Obviously there would be less competition, but still...there IS competition. Sprint and Verizon aren't going to just sit by and let this happen. If At&t buy t-mobile, then there is a large chance verizon buys sprint. The govt isn't going to allow at&t to buy t-mobile and then turn around and not let verizon buy sprint.
It seems the fate of many industries is to become a duopoly only because the government won't allow a monopoly. Look at microsoft vs. apple, UPS vs FedEx, pepsi vs. coca-cola, boeing vs airbus, intel vs amd, democrats vs republicans, crips vs. bloods, and the list goes on and on.