Why not just store the contact info on a web app? I know that some PHP and ASP programs out there will do email clients on a local Intranet. Then you can modify the code to share contacts, etc.

If my skills where up to date and I had the time, I'd write a web based alternative to Outlook in ASP or ASP.NET and then maybe port it to PHP or JSP. Anyone done this yet?

The only thing with Outlook that prevents it from being used as a Corp email client is that hardly any other email client can work with Exchange Server. D'oh!