Wild Card vs. UC Certificates
Exchange 2007 and Office Communications Server 2007 have strict requirements for x.509 certificates..Wild card Certificates can't be used as these will break TLS for the edge servers. The edge servers need FQDN for proper operation. This can be accomplished with SANs. Multiple SANs can be supported with UC certificates.
Our KB article (kb929395) lists some of the providers of these UC certs....http://support.microsoft.com/kb/929395
