Microsoft has released a knowledgebase article to inform customers of an upcoming server move being performed by Yahoo!. This move could impact your Public Internet Connectivity (PIC) availability with Yahoo!. This move will only impact PIC if you have your firewall configured to limit port 5061 connectivity based upon IP address. Check out Microsoft Knowledgebase article 952209 for the full details.

Source: Microsoft Knowledgebase Article 952209.