hi,
I have done many projects like that, i have build elastix 2.2.0 in centos 5.7(this is requirement) in EC2, fortatrust vps.
in elastix, we got hylafax, fax guide too(if you need avantfax, it is ok. i am done this project some days ago, waiting customer to test it. )
contact me to get it works and function.