In the last newsletter we discussed a few of the details of AT&T\u2019s certification of Cisco and Avaya IP PBXs for interoperability with AT&T\u2019s IP services. This time, we want to examine the impact of this announcement.To us, the major impact is bringing additional credibility to this market. Some of you may remember that back in the early 1990s when AT&T introduced its frame relay service, it wasn\u2019t first to the market. Frame relay was already readily available from CompuServe and WilTel.But the market really took off after AT&T announced its service, because this gave legitimacy to the concept - and all of a sudden frame relay was on the way to becoming a mainstream service.Even though it\u2019s arguable whether AT&T still holds such influence as it did 12 years ago, there\u2019s no question that this announcement is important. It\u2019s probably more important for \u201cvoice people\u201d than for \u201cdata people,\u201d since the more traditional voice administrators tend to be more skeptical about whether voice over IP (VoIP) is ready for prime time.The bottom line? From a technical perspective, this is not a major milestone. It also doesn\u2019t mean that you\u2019ll save 90% on off-net toll charges. And it doesn\u2019t even start to address full interoperability among VoIP networks. But it\u2019s quite significant in the integration of IP PBXs with WAN voice services - and in the evolution of VoIP from a cool niche technology to a mainstream service.