I was completely opposed to the merger on the basis that this country needs more carriers, not fewer. I travel internationally a fair bit and having been around, I think the US (and Canada) have two of the worst cell phone systems that I've seen in terms of what you get for what you pay for, particularly in terms of text messages and data (voice actually isn't too bad). You could say that it's because of the size of the country, but other large countries like Russia and Australia have less expensive data, texting and voice plans and prepaid than the US.
The first time that I remember thinking that we already have too few carriers in the US was when Sprint raised it's per-message texting rate from $0.10 per message to $0.20 per message several years ago... and then within days or weeks AT&T and Verizon did the same, and soon after T-Mobile did as well. So the question is, what caused this rate increase, and why did all of the other carriers feel justified in increasing their rates as well. In the airline industry, I see airlines do this - they will all raise rates - and then you'll see one carrier say "no, we are sticking to our current pricing" and the other airlines with back down on their rate increase or not. To me, this is something closer to a free market system. But with cell phones, if one carrier decides that the minimum number of minutes on their plan is going up from $30/month for 300 minutes to $40/month for is 400 minutes, then all of the others change so that their plans match... with the occasional exception of T-Mobile.
Price out a phone, data and texting plan and you will see that there is very little difference between the carriers and that this difference has not really changed over time - when one raises rates, the other do too. I think we need two or three more nationwide cell phone carriers, instead of one less.
In particular, T-Mobile is one of the better prepaid and bring-you-own-phone vendors. You can get an calling and unlimited texting plan from them for $15/month - that's it... $15 total and you can get you teenager a phone without having to add them to your plan and worry about them blowing your bill away because they are silly.
To me, the net benifit of an AT&T/T-Mobile merger was in favor of AT&T as a company. They gain T-Mobile's customers and towers, they gain T-Mobile's spectrum, on a system that is fairly compatible with their own. And for this, they pay an amount that is really not too expensive compared to what these things are separately. From a customer's perspective, the customers gets better service, but we lose a competitor to keep prices down.
I personally thought that it was a net loss from the consumer's perspective, and I wrote several letters to my senators, and my congressional representative. I attended a Q&A session with my congressperson and asked them about the merger. I wrote a comment letter of opposition to the FCC, and I wrote letters to the editors, signed petitions, and was quoted in the Denver Post. I think this is a good thing and I can't think of any other carrier or company that would be a bad merger for T-Mobile except for Verizon and so I look forward to seeing what happens next with a feeling that anything that happens is likely to be better for T-Mobile customers, and the US cell phone market, than AT&T and T-Mobile combined.