$39 Billion. It makes sense that the cell phone market will always be an oligopoly, at least as long as the carriers have leased the spectrum from the public. But I think that 3 carriers is too few, and I hope the SEC agrees. If the options are allowing the merger or disallowing it and watching T-Mobile fail, it's certainly better to allow the merger. Especially since the assets would be bought by Verizon, Sprint, or AT&T at firesale prices and we'd have the same result.
In a decade or three, once the technology and market has matured into a commodity, it will probably make sense to split the stewardship of the frequency spectrum and the carriage of the data into separate markets, possibly with greater governmental oversight or control of the "last-mile" airwaves. But for now it's all moving too fast. The market has been driving innovation forward pretty damn fast the past few years and it'll be nice to see that continue.
That said, three isn't enough. There are other bit players, but this really just leaves AT&T, Verizon, and Sprint. Having been a customer of all three, I can't say I enthusiastically recommend any of them. My experience hasn't been especially bad, but at best I'd describe them as "adequate". I'm quite sure that the combined AT&T/T-Mobile monster won't be better for consumers than AT&T and T-Mobile competing. At least this merger is a clear win for somebody: Apple.