You can jail break the phone to get alternative apps. But you're right, unlocking is less sexy for U.S. users...
Not to mention that Tmo and ATT offer 3G on different frequencies here in the US. For this reason, even if you unlock the iphone for use on Tmo it will only get GSM/EDGE for data. To be honest if you are deadset on using an iphone on Tmo, you might as well save some money and buy an unlocked 2G version. -- Комитет государственной безопасности
