This works....I've done it on two iPhone 4s on 4.0.1, 4.0.2, 4.1, and 4.2.1. I've used it on at least three 3gs iPhones on 4.2.1. People keep having issues but this will fix it if you follow the directions exactly. Note you must UNINSTALL any mms patches you've installed before AND reset network settings before you try patching via these instructions.