Exchange 2010 UM no longer handles the inbound fax negotiation, if a fax tone is heard, the call is handed off to a fax solution via the solutions URI. This means if you’re receiving faxes currently and you’re going to upgrade to 2010, you need to be watching this space for announcements on partner solutions as they appear.
How could this be a good thing?
Well, considering that all the 2007 UM role did was receive faxes, wouldn’t it be nice if you no longer had duplication with your enterprise faxing solution and could take advantage of what both solutions did best ? I’m never a fan of partial solutions, and since we only had incoming fax capability in 2007 - and nothing else - , having an integration path to a partner solution suits most folks much better than Microsoft building a fax solution from the ground up.