So many partners are trying to figure out which ITSP’s and Carriers’ SIP trunking services are tested/approved to work with Avaya IP Office and Avaya Communication Manager. As you may know, SIP is a surprisingly loose standard so interoperability becomes pretty important to pay attention to. I’m not sure Avaya does the best job of making it known which providers have a green light, so it took a little digging around for me to cobble together a matrix of approved SIP trunking providers for IP Office and ACM — by the way, some are approved for IP Office and not for ACM (and vice-versa).  I’ll release an updated version of this soon with more details for comparison. See below..