Remember a few days back when we told you that the iPhone 5 is now available for pre-order on T-Mobile? If so, you’ll also remember that we mentioned upgrading could be a costly move  since the company recently decided to do away with contracts, meaning users will have to pay full-price for phones from now on.

However, as Mashable recently reported, the mobile underdog understands that, while the latest iPhone model is desirable, throwing down the $100 down payment isn’t necessarily something the average user is ready to do, especially if they’re looking for a contract-free mobile solution.

So how did T-Mobile respond? By inviting iPhone 4 and 4S owners to trade in their used devices as a down payment on their brand spanking new iPhone 5. To boot, the company will also evaluate the value of the phone being traded in, giving customers as much as $120 worth of credit that can be used toward monthly payments, an existing bill, or even accessories to accompany that new phone.

If not for this offer, anyone wanting a contract-free iPhone 5 with T-Mobile will have to be willing to pay $100 (for the cheapest model) upfront, and then spend the next two years paying $20 a month, on top of a monthly cell bill, to pay off the phone. But those taking advantage of this offer can steer clear of the down payment, and only pay $15 a month for their new phone.

Still not sure you’re willing to make the move from your current provider to T-Mobile? There’s plenty of time for you to decide. This offer is going to be available until June 16.