Questions[unified-communications](server)

I've seen several brief articles on the Microsoft Lync server (formerly Office Communications Server) that talk about replacing PBX's, but in reading some press releases and websites I'm not finding it clear exactly what Lync actually does and doesn't do.

Can someone please tell me if Lync can perform the same functions and replace a linux-based Asterisk PBX? I've got an existing Asterisk PBX and VOIP phones I'd love to switch to a Windows-based system. I'd be looking for normal PBX functionality (e.g. voicemail, autoattendent).

Thanks!

Is it possible to install the mediation server component of Office Communication Server 2007 R2 on to the same hardware as the front end server component, or do I need additional hardware?

If it is possible, what would be the user limit before the roles needed splitting onto separate hardware? (assume I'm using fairly good hardware, i.e. Fast Xeon CPUs, lots of memory, 64 bit Windows 2008).

Are Unified Communications SSL certificates (aka Subject Alternative Name / SAN) suitable for securing a CMS website in IIS, which serves lots of different secured websites for various clients each on their own domain name? The CMS will run on a single IP address and a single IIS site, but the content served will be different based on the host header / domain.

I understand that this is technically possible, but I'm interested to know if anyone thinks this is bad practice or a potential security issue to share an SSL certificate for many clients?

Thanks, Tim