IBM's approach to unified communications is anchored around applications, an important distinction from the current state of Microsoft's effort which has been more centric to platform convergence. It makes sense, IBM still has some foundational work to do on the backend of Sametime and Microsoft is more interested in consolidating infrastructure at the moment than application enablement.
This post highlights the Sametime 7.5 plug-in and integration with Asterisk (an open source PBX). Since the plug-in model is based on Eclipse, this integration will work for other Eclipise-based client such as the forthcoming "Hannover" release. The iscoord plug-in is interesting enough but what is also intriguing is Asterisk's ongoing work with XMPP and Jingle as well as SIP.
IBM is currently embracing SIP/SIMPLE, but providing a unified communication framework that enables enterprises to "plug in" interfaces that exploit XMPP and Jingle if necessary (for access to consumer environments) is another point of differentiation from Microsoft that IBM should highlight more strongly. Note: IBM has already pointed out that its new gateway for federating IM and presence to external networks will support public IM networks such as Google (which is based on XMPP and Jingle).
Source: Adam Gartenberg's Blog