T-Mobile started carrying the iPhone last month for $99 upfront and $20 equal monthly payments over 24 months, but it has now raised the down payment to $149.

The iPhone finally launched on the carrier's network after T-Mobile announced its "UNcarrier" plans, which allowed customers to essentially get a 16GB iPhone 5 for a down payment of just $99. What was not exactly clear, however, is that the $99 price tag was actually promotional, and the promotion is now over.

T-Mobile raised the price of the iPhone 5 to $149 upfront, while the $20 monthly payments over two years remain in place. Under the regular pricing structure that went into effect on Monday, May 13, the iPhone 5 now costs a total of $629 spread across 24 months, up from the promotional $579 total cost.

The 32GB and 64GB models are getting new price tags as well, moving up to a $249 and $349 upfront fee, respectively. That's a $50 increase in the net down payment across the board.

T-Mobile is the fourth largest wireless carrier in the U.S. and the last of the "Big Four" to nail down a contract with the Cupertino giant. According to T-Mobile, it sold more than 500,000 iPhones since the device launched on its network on April 12.

On the other hand, the fact that the monthly fee for the iPhone remains at $20 for 24 months still allows T-Mobile to claim it offers the most affordable upfront price currently available on the market. The iPhone always enjoyed great popularity, and its absence from T-Mobile's network was criticized by many. Now that T-Mobile is finally on board with Apple's smartphone, things are looking up, but raising prices after an unknown promotional period is bound to raise some further criticism.

The iPhone trade-in offer, meanwhile, saw an uptick in marketing over Mother's Day weekend and continues to offer customers a great way to offset the upfront cost of upgrading to an iPhone 5 by bringing in their old iPhone 4 and iPhone 4S handsets. Under the iPhone Guaranteed Trade-In Offer, T-Mobile offers the iPhone 5 for no upfront cost in exchange for old iPhone 4 or 4S smartphones. The $20 monthly payments remain the same.