FAX + VoIP - T.30 / T.38

Ok... just discovered the 2-sided discussion on Fax over IP.
Some VoIP vendors indicate they have not seen any probs over their
network,
while some integrators have said flat out it doesn't work reliably...

SO - what's been your experience with normal FAX machines
that work fine on a POTS/PSTN network...
plugging them into an analog port on a VoIP gateway,
and used across the VoIP LAN / WAN con ..
Telecom, Cabling and VoIP continues...
Tags: Telecom VoIP Networking Internet cat6