Sometimes due to various reasons you may get error messages when you are installing APN Settings (from here or other websites). The errors may include the ones below.
“Only one APN configuration can be installed at a time”
“Cannot Install Profile. Safari could not install a profile due to an unknown error”
Normally these errors may be fixed by uninstalling previous APN Settings Profile from Settings->General->Profiles.
If this doesn’t work a full restore and then installing the APN Settings again (before you sync with itunes)