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.

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