- Single sign-in. Users can now connect their Office Communicator Phone Edition phone to their computer with a USB cable and sign in to both their phone and Office Communicator 2007 R2 at the same time.
- Integration with Office Communicator 2007 R2 on the PC. Users can now click a contact or phone number in their Office Communicator 2007 R2 contact list on their PC to place a call using their Office Communicator Phone Edition phone. Call controls are synchronized on both the phone and Office Communicator on the PC. If their PC is configured with a webcam, users can escalate the call by adding video.
- Support for new Office Communications Server 2007 R2 voice features. New call delegation, team calling and Response Group service functionality in Office Communications Server 2007 R2 are also supported in Office Communicator Phone Edition.
- Audio quality enhancements. Latency, audio quality and call setup time have all been improved.
- User interface enhancements. The user interface has been improved and streamlined. For example, a Redial button enables users to easily redial the last dialed number, searching through the corporate directory is easier, and users can select from one of four ring tones.
- Office Live Meeting support. Users can now use their Office Communicator Phone Edition phone as an audio device in Office Live Meeting.
Get more info (and my source) here