We use Lync 2010 with our ShoreTel VoIP phone system and random people get a third number added to their group conversations when making phone calls and it doesn't happen every time. The calls are not initiated through Lync but do show in Lync since its
tied into the phone system (ShoreTel CSTA). The same number shows up for everyone and its not even associated with anyone we know. The person is not on the call with the 2 internal people and their phone does not ring (we called the number).