Microsoft have given a few warnings recently about changes who restrict PIC traffic via IP address lockdown. Here is the final update as the changes happen tomorrow!
This is the one week reminder that the scheduled additional IP Address is on track for implementation on Friday, March 26, 2010. For organizations restricting this traffic to specific IP addresses the updated list in the KB below MUST be in place by March 26, 2010 or PIC connectivity to MSN WILL fail.
897567 Known issues that occur with public instant messaging and Communications Server
Barring an unforeseen issues, this is the final notification on this change.