When will T-Mobile end 3G support on AWS?

For various reasons, we're looking to buy my wife a new phone. We're happy T-Mobile customers (at least where I am, I get better data speeds from T-Mobile than on Verizon LTE), and she was looking at a Galaxy S III. Looking over the specs, I was surprised that there's no HSPA+ on the 1900Mhz band, where T-Mobile is migrating their (cough) 3G to free up spectrum on AWS for their LTE rollout. My question is, have T-Mobile said when, or if, they're intending to kill 3G on AWS? I assume this'll happen eventually, and I expect we'll want to be able to use this phone for 2-2 1/2 years before replacing it. If 3G on the AWS band goes before then, we'll end up with an expensive paperweight.

Any news on this? Or will TMo keep HSPA+ running on AWS alongside their LTE network?