With the way CDMA works u won't find it easy to get a unlock since there isn't one. Some phones can be flashed to be able to use the SIM card like the Blackberry Storm can be used on T-Mobile. Cricket will flash the iPhone 4 to run on their network. Flashed phones are buggy tho. Plus CDMA carriers usually don't like a phone from a different network on their network. GSM phones use the sim card to communicate to the network while CDMA technology uses a chip that is built into the phone itself and the ESN is hard-coded with your phone’s information so it can communicate with the network. Modifying that chip would be like modifying your SIM card’s IMEI number and is completely illegal.