No. 4 wireless carrier T-Mobile today detailed a new trade-in offer targeting Apple (AAPL 1.27%) iPhone users in an attempt to get customers to switch from other carriers.

Prospective defectors can bring an iPhone 4 or iPhone 4S from another network and trade it in to cover the down payment on a new iPhone 5 on T-Mobile's network, reducing the upfront device cost to $0 for "well-qualified" customers.

The offer will run through Father's Day, June 16, and T-Mobile said customers can potentially receive an additional credit of up to $120, depending on the value of the device that they're trading in. That credit can be used toward monthly payments.

T-Mobile launches the iPhone 5 this Friday.

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