AT&T TR1909 - Manual (Page 8)

7
Installation options
Wall installation
To install the telephone base in the wall-mount position, make
sure that you first unplug the telephone line cord from the
telephone wall jack and remove it from the channel.
1. Lift the handset and place it aside. On the telephone base, pull
out the handset tab and rotate it 180 degrees. Replace the
handset tab back to the grooves until it clicks into position.
Your telephone base is ready for tabletop use. If you want to
mount your telephone on a wall, use the provided wall-mount
bracket to connect with a standard dual-stud telephone wall-
mounting plate. If you do not have this mounting plate, you
can purchase one from many hardware or consumer electronic
retailers. You might need a professional to install the mounting
plate.