FreePBX 12 is currently in beta testing but there is an option on FreePBX v2.11 called “FreePBX Upgrader” to allow upgrading to FreePBX 12. It is not overly obvious that this currently upgrades you to a beta version.
If you are running on CentOS 5 it is recommended that you do not run this update as it will break your FreePBX install.
This is caused by the way that the module update routine checks for available updates (using wget -q).
There is no intention to fix this issue so FreePBX 12 will not run on CentOS 5 (without some manual intervention). More details about this can be found here – http://issues.freepbx.org/browse/FREEPBX-7994