There are certain codes and ways available to check various options in our mobile. This applies to Nokia and Sony Ericsson mobiles as well. Following can give you some basic codes/ways to find those

Nokia Mobiles:

All Nokia mobile users can use the following codes to find the details,
1. To check the version use *#0000# which will display the version used in the model and year of make. When this code is not working use *3370#.
2. To get the security code of the mobile use *#2640#.
3. When you are in need to see the private number use *#30# which helps you in finding the same.
4. To activate/deactivate Enhanced Full Rate Codec(EFR) follow
- *3370# to ACTIVATE
- #3370# to DEACTIVATE

5. To check the IME (International Mobile Equipment) number use *#06#. This IME number is unique for all the mobiles and it helps in tracking out your mobile when it is lost.
6. To switch between LINE 1 and 2 press and hold # for quite a few seconds.
7. If you are in need to restore the factory settings use *#7780#. This restores the mobile to the original mode i.e. to the initial make mode.
8. To check the amount of hours spoken in the mobile use *#92702689#. This displays the amount of hours spoke but in some models the mobile needs to be switched off after checking this.
9. To turn on “All calls” to a particular number use **21*number#. For “No Reply” use **61*number# and for “Busy” use **67*number#.

Sony Ericsson:

To know all the above mentioned details use the following steps
1. There will be joystick in all the Sony models which helps in checking. Press RIGHT and press *
2. LEFT-> LEFT->*
3. LEFT->*
4. These steps will take you to a menu which has all the options. You can select any option from this and check it. It has many things like spoken hours, service test etc.

5. To check the Lock status use: <- * * <-
6. To go to the call list use 0 and # on the main menu.
7. To open any numbers stored on the sim type a number and press # on the main menu.

* If you know any other tricks than these please post it in the comments section.