I don't think this is a good idea for customers. Even Sprint acquiring T-mobile is a bad idea, but this is much worse. At least with Sprint buying T-mobile you'd have 3 equal sized companies, but in this case, I wouldn't be surprised if Sprint eventually gets bought by Verizon, and then Americans will really be in trouble.
That would be unlikely (or at least, less likely) considering that Sprint uses CDMA, while AT&T uses GSM. T-Mobile's network would be easier for AT&T to integrate.
