Sony Ericsson K500i & Sony Ericsson K700i

Service Menu - >*<<*<*
Shows you hidden items

Firmware Info - >*<<*<*11
Shows which firmware you are using

Silent Mode - "#" or "C"
Puts your phone quickly in Silent Mode or disables it

Sony Ericsson P800
Service Menu - Jog dial Up -> * -> Down-> Down-> * -> Down-> *

Silent Mode(when flip attached) - Press C button on Flip

Menu Key(when flip attached) - Keylock on/off, Silent on/off, Calls, status, Applications

Speaker Phone(when flip attached) -
When on call Open Flip, close to off Speaker Phone

Show IMEI - *#06#

Volume Adjust - When On call, Move the Jog Dial for Volume Increase
Move jog dial down for Volume Decrease

Busy Tone
When receiving a Call to send a busy tone to the caller press the Jog dial Outwards.

MMS navigating
While going through a MMS, turn up & down to go within the pages.