Panasonic kx-td7896 how do i unlock the phone?

SOURCE: This is really silly, but

hold the * button... There should be a small M right beside it. (M= mute)

SOURCE: This is really silly, but

HOLD DOWN the "M" key which is the "*" key in the bottom left for 3 seconds until you hear a beep.  Repeat if you want mute again.
Jack

SOURCE: the phone is dead even with new battery installed

the batery connector may be faulty you have to change it

SOURCE: how to unlock panasonic kx tg1070 cordless phone

Cant unlock phone

SOURCE: I recently bought a Panasonic

Does page 16 of this PDF offer any useful information?

http://www.smarthomeusa.com/Products/KX-TD7896/manuals/PanasonicKXTD7896.pdf