You can use your mobile phone (MP) as a dialer if you need to make a call and the land line phone's (LP) keypad is locked. Simply go to the engineering menu of your MP, go to the diagnostic menu and select the earphone or speaker test. Then, simply put your MP's earpiece to the LP's mouth piece and dial the number on your MP.

Note: This can be very useful if you need to make and emergency phone call, you're a cheapskate, or as a party trick. This trick is here purely for it's educational value and should not be misused. This trick might also be illegal in your country.