The Idea is to have a t38modem + Hylafax running as a beroFix App. It’s quite hard to cross compile t38modem and even harder hylafax.
t38modem is done now and runs on beroFix 
hylafax is in progress. Unfortunately Hylafax is not prepared for cross-compilation at all.
I did some tests with efax and could transmit a hello world fax already