The last of the four major carriers in the U.S. to get the iPhone is T-Mobile, who are now offering pre-orders for the iPhone 5. T-Mobile also offers the lowest up-front cost, of just $99 (plus monthly payments of $20 for 24 months). They’re also offering the iPhone 4S and iPhone 4 at slightly lower costs for those who are on a tight budget. Pre-orders will begin shipping on April 12th, and should be available in T-Mobile stores. You’ll find more pre-order information here.