Siemens S6/S10

In Phonebook, store as your own number: +12022243121
Then you get the sun and two palms in the display, also a greeting message of the "MMI-team".
It has been said that the phone number is the number of the Capitol building in Washington, DC (but not sure).

Siemens S15 Secret Menu's

Press * -> # -> 7 -> 4 -> 3 -> 6 -> 3 -> 6 -> 7 -> * -> 8 -> 3 ->
7 -> 8 -> # ,press clear key to clear screen and return to
stand-by mode
press Menu, it will show additional menu
Menu 3.3.4 Band selection,
Menu 3.3.4.1 Automatic band selection,
Menu 3.3.4.2 select GSM 900 only,
Menu 3.3.4.3 select GSM 1800 only,

Menu 10 Engineering,
Menu 10.1 MS info,

Menu 10.2 software detail,
Menu 10.2.1 software version,
Menu 10.2.2 EEPROM version,

Menu 10.3 Test/production details
Menu 10.3.1 Hardware deta
Menu 10.3.2 production deta
Menu 10.3.3 Service deta
Menu 10.3.4 Mechanical deta

Menu 10.1.1 MS info on, then on the screen show these, for example:

FCN RXL C1 C2
642 011+11+91 -> PAGE 1