I was wondering if it was possible to start a new Office Communicator conversation from a link in the same way that you can start start a new email with the "MAILTO:" link. I am mostly looking to do this from within Outlook 2010.
in addition to the SIP: uri mentioned from bquaresma, if you have telephone integration, you can also use the tel: uri to make a phone call. In my outlook signature, I have my phone number as tel:+15551234567 Outlook just shows it as 55501234567. When people click on it, it initiates a phone call to me.