PocketSensor locks your S60 phone using proximity sensor

[wraggster]

PocketSensor by PhonePhreak Software uses your phone's built-in proximity sensor to automatically lock the phone when it is put in a pocket. No need to bother with the lock slider any more!

http://my-symbian.com/s60v3/software/applications.php?name=PocketSensor_Automatic_Keylo ck&fldAuto=792&faq=1