Please keep in mind that the fax features of UM are not supported together with OCS 2007. The OCS mediation server does not support the fax codecs nor does it support allowing media to flow directly between the voice gateway and the UM Servers when fax is detected. (Tip-Paul T.)
The suggested deployment mode is to split the numbes associated with fax at the media gateway or in front of it with an ISFN splitter and to direct those calls to a T.38 gateway. ( TIP-Francois)