T-Mobile has added yet another incentive for prospective customers mulling a switch to the uncarrier. The company will offer an iPhone trade-in program as part of its sale of the iPhone 5. 

The trade-in offer, which begins April 12 and runs through Father’s Day on June 16, enables customers who bring in their iPhone 4S or iPhone 4 to get iPhone 5 for $0 down plus monthly payments, with a no annual service contract Simple Choice Plan. 

Depending on the trade-in value of their device, customers will also receive a credit of up to $120, which can be used toward monthly payments, an existing T-Mobile bill, or the purchase of accessories or another device.

 Through its Simple Choice Plan, T-Mobile is the only major U.S. wireless company offering iPhone 5 with no annual service contract plus unlimited talk, text and Web on a screaming-fast nationwide 4G network.

T-Mobile is currently pricing the iPhone 5 at $99, with additional payments of $20 per month for 24 months. 

The trade-in comes as competitors in the prepaid space have perked their ears to T-Mobile nixes subsidies and contracts from its business model. Just yesterday, Sprint Nextel's Virgin Mobile prepaid business launched a campaing that offers T-Mobile users a $100 credit to switch carriers. A large banner ad on Virgin Mobile's homepage beckons, "Ditch T-Mobile and Get a $100 Credit."