Most Android phones have a “Unknown Sources” toggle. Once this is checked, you can install Android Applications from anywhere. If this is not checked, your phone won’t install anything that isn't from the Android Market. Starting with their very first Android phone, AT&T has completely blocked this option to install non-market apps. Thanks to nagging, or because AT&T realized this was a horrible idea, the policy of blocking non-market apps has been reversed. Starting with the Samsung Infuse 4G, AT&T Android devices will now be able to install third party apps from non-Android Market sources. Hopefully all the AT&T Android devices floating out there will be updated accordingly.