"On the fax issue, it is well documented that the circuit-switched fax protocol, T.30, does not fare well on an IP packet network where SIP trunks live. Packet loss and jitter are unkind to fax image data when it is treated as an in-band pass through audio transmission using SIP and RTP. Failure rates grow at an increasing rate as individual fax document lengths increase, and those failure rates are generally deemed unacceptable for any production fax environment where images are part of an automated workflow. Yet ensuring support for the T.38 protocol, which enables reliable FoIP, is frequently a lower priority in the race to offer SIP services to the enterprise."
On deplyment: "Interoperability, security, network address translation and firewall traversal, legacy switch integration and demarcation are all areas that should be resolved prior to deploying new services."