LG G2x / Optimus 2x

A phone like this becoming obsolete will only happen in two years' time - at the soonest - at which point you'll probably be shopping for a new phone anyway, and enjoying a discounted contract-renewal price.

Remember that nothing at all will happen for 12 months. That's how long they will remain 100% separate companies. After that, they've announced that they will "dual-band" most of their towers, meaning WCDMA 1700 coverage will actually increase at first, and phones like this will work better than ever.

Eventually they will phase out WCDMA 1700, but only after the companies have merged and they've stopped selling WCDMA 1700 phones for a year or two.

If they wait less than two years after WCDMA 1700 phones disappear from store shelves, they'll have to offer steep discounts for people to upgrade to the new WCDMA 850/1900 smartphone of their choice.

Bottom line: there's nothing to worry about. Buy a WCDMA 1700 phone. By the time AT&T decides it's obsolete, you'll probably think it's obsolete, too.