Today's the day, folks. Those wanting an iPhone 5 on T-Mobile can now order one on T-Mobile's website with a ship date of April 12. You can grab one for as low $99 down, with monthly payments of $20 per month for 24 months. Or, if you have the cash, you can pay in full at checkout for as low as $579 for the 16GB model. Join that together with a $50-per-month plan and you really got something.