Hi.
I'm not using this contrib (if you speak about smerpfax), but I'm using hylafax, with smeserver-hylafax from dungog, and some customization. With this, I've installed iaxmodem rpm from trixbox repository (I even recompiled the binary iaxmodem to have the latest version). It's working with asterisk, I can send and receive faxs through my pstn line with no problem. You just need to create a iax extension in asterisk. then configure iaxmodem to use this account (in /etc/iaxmodem/iaxmodem-cfg.ttyIAX). Once this is done, configure hylafax to use the iaxmodem
faxaddmodem ttyIAX
You can let the default answer for most of the question.