With its recent acquisition of PostPath, a maker of e-mail and calendaring software, the word on the street is that Cisco is positioning to strike at Microsoft's Exchange crown jewels.
This is not inconsequential for "Microsoft shops' looking for UC solutions.
Cisco has been telling enterprises to buy their UC now, and that interoperability with Exchange/OCS environments will come later.
The relationship between Cisco and Microsoft is already pretty precarious on the UC front with competing UC solutions. Given that Exchange is very tightly linked to Microsoft's UC strategy, the likelihood of any meaningful interoperability is increasingly doubtful.
Contrast that with the alliance between Nortel and Microsoft. The Nortel Converged Office for the Communications Server 1000 is the first and only fully qualified IP PBX for integration with Microsoft OCS 2007.