If you've been eying that 64GB HTC One on AT&T, but don't exactly relish in the thought of dropping 300 big ones to get your hands on it, there may be another option - AT&T just announced that it's running a smartphone trade-in promotion that starts tomorrow.

Here's the fine print: you need to trade in a working smartphone less than three years old in "good condition." And yes, the last part is pretty subjective. $100 is the minimum value if you meet those requirements, so you might actually get a little more if your smartphone is particularly new. Though, if it's new enough to be worth more than $100 to AT&T, you're probably a lot better off selling it yourself.

There are a whole lot of old smartphones that could qualify for this promo, and many of those closer to the three-year-old mark can barely fetch $100 on the open market. If it turns on and is in one relatively good-looking piece, AT&T will hand you a $100 credit. This deal is available to both new and existing customers. AT&T is also accepting old feature phones, data cards, and tablets for AT&T promotional credit, though the value of those items will obviously vary widely.

The credit can be applied immediately (in AT&T corporate stores) to your purchase of any new smartphone on AT&T. That drops the 32GB One and 16GB Galaxy S4 to $100 on contract, respectively, and the 64GB HTC One down to $200. There's also nothing here indicating that you couldn't apply this credit to an off-contract smartphone purchase. You can even trade in multiple smartphones in a single visit.

This offer is going on for "a limited time" (I'd guess a month), so if you're in the market for a new phone on AT&T, it may be worth taking advantage of.

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