SIM unlock codes are not available from AT&T for 10 months after release of AT&T "exclusive" phones (includint the Inspire). The Inspire was released Feb. 5, 2011. So that's not for another 5 months. After that, as long as you have been a customer for 90 days, you should be able to call customer service and request the code.
If you need the phone unlocked earlier, the easiest method is probably to buy a code online. They are easily found on eBay, for around $10. Just pick a seller with a good rating.