The beta is underway for Microsoft’s new communication suite, code named “Istanbul”. The new software will offer it’s users instant messaging, PC-Based voice and video along with telephony capabilities. Istanbul will look like MSN Messenger and will allow linking to AIM and Yahoo chat.

Here is the statement released from Microsoft. 
As the preferred client for Microsoft Office Live Communications Server, "Istanbul" will enhance the business user experience by:

• Enhancing presence and real-time collaboration. With "Istanbul," presence becomes richer as additional availability data, including out-of-office information, is included. In addition, users are able to control their communications based on their presence.
  
• Improving usability. "Istanbul" will help business users take advantage of advanced communications capabilities more easily by consolidating applications into a single interface including instant messaging, conferencing and traditional telephony.
  
• Member of the Microsoft Office System. With "Istanbul" and Live Communications Server, presence and communications capabilities become a richer part of the Microsoft Office experience, including integration with Microsoft Office Live Meeting. End users will be able to initiate collaboration directly from their already familiar desktop applications.