If you're not familiar with Microsoft Lync, don't feel bad - I had no idea what it was before today, either. Makes sense, because I don't work in an environment where Lync is used (or would be useful), but for those who do, it's actually pretty cool. In a nutshell, it's an IM/contact management/VoIP client used for Exchange - think MSN Messenger with a GTalk twist built for the corporate environment .
The Android version allows you to see your colleagues' availability on-the-go, as well as initiation an instant message, email, or phone call directly from the app. You can also connect to Lync conference calls quickly and easily - no passcodes or conference numbers required. Going to be out of the office for a while? No biggie, you can use Lync to either forward calls to your mobile, or have it ring both numbers at the same time.
The app is free in the Market, but you must have Lync Server or Office 365/Lync Online to be able to use it.