If you hear another phone ringing, there are a number of ways that you can answer the call if you know the user, group or line being called.

To pickup a call ringing elsewhere:

1.When you hear the other extension ringing:

To pickup a call ringing at a particular extension:
Dial 6 followed by the extension number at which the call is ringing or parked.

To pickup the longest waiting call in a pickup group:
Dial 66 followed by the pickup group number (1 to 4).

To pickup the call ringing on a particular line:
Dial 68 followed by the two digit line number.