FreePBX Version 12.0 Supports Asterisk 1.8, 10, 11 and 12.

Supported/Tested *nix Distributions 
DistributionDate Last TestedCertifiedTestedCommercial Module SupportNotes
CentOS 6.512-16-2014NoYesYes (Install)The "recommended" distribution for FreePBX
Ubuntu Server 14.04 LTS6-20-2014NoYesNo 
Ubuntu Server 14.1011-02-2014NoYesNo