Cannot get a2billing working with FreePBX 10

I have a problem with getting A2Billing to work with the FreePBX ISO. I am able to get all my extensions, outbound routes etc to work perfectly in FreePBX. Tying to get the required packages for A2billing poses compatibility problems. I have searched many forums for a solution but haven’t found anthing specific. php-mcrypt e.g which is listed as a requirement will not install. Has anyone tried replacing the version of php that comes with the distro or does anyone have a link to instructions that work for the installation?

I used a minimal install of CentOS 6.3 with Asterisk 10.6.1 and FreePBX 2.10 with A2Billing 1.9.4 and got it up and running in 15 minutes