If you have been using the T20 and it no longer makes any sound out of the ear piece, it could be a sign of a faulty headset speaker. Try connecting the headset to another T20 base to learn if the headset is the problem.
If this is a new installation, note that the T20 is an analog 2-line phone which cannot work in place of a digital phone in office environments. However, some digital phone systems can provide an analog extension which will work with the T20; check with your phone or IT manager to learn if you phone system supports analog extension.
For phone line connections and installation instructions click here.