I'm guessing it's just wearing out over time and use, but is there anything you can do for a cordless house phone key pad that has numbers that frequently stick.
Take it apart and check the rubber pad to see if you got any liquid in it, do mine all the time ... usually my daughter gets soda or something on the phone. I usually clean the contacts where the pad is pushed down with a wet q-tip and then wipe it the same way with a little wd40 on the q-tip and it's good for another month or 2 until she makes a mess again.
Insanity is a long and winding road ... I think I finally made it there.