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AT&T Developer ProgramT-Mobile isn’t the only carrier offering sweet trade-in deals.

Starting Wednesday, AT&T is offering at least $100 in trade-in credit for those who swap their smartphone and purchase a new one via AT&T, including the Samsung Galaxy S4, the Blackberry Z10 and the HTC One.

Your trade-in phone must be less than three years old and in “good, working condition.” AT&T is also offering more than $100 for certain devices — you’ll have to go to a retail store or check online to find out how much your phone is worth.

Earlier this month, Bellevue-based T-Mobile announced a new offer to provide an iPhone 5 for $0/down to people who trade in an iPhone 4 or 4S. Customers will still need to make monthly payments for the device, in addition to their wireless service payments, but T-Mobile says it will also offer a credit of up to $120 depending on trade-in value, which can be used to further reduce that monthly bill. The trade-in offer runs through June 16.

Sprint and Verizon are also offering similar trade-in deals.

Previously on GeekWire: Safety first: AT&T debuts remote monitoring home security system in 15 markets

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