Loads of hidden menus, diagnostic feedback, wireless network information, and much more without installing any applications, it is as simple as using your numeric keypad and activating the phones hidden treasures.
Not all Android devices support all codes, and some are are only for series or individual devices, but you came give them a quick try.
1. *#06# – IMEI number
2. *#0*# – Service menu on devices like the Galaxy S III
3. *#*#4636#*#* – Information about device, user statistics and battery
4. *#*#34971539#*#* – Details on camera
5. *#*#273282*255*663282*#*#* –Instant backup media files
6. *#*#197328640#*#* – Activating test mode devices
7. *#*#232339#*#* – Test for Wireless LAN
8. *#*#0842#*#* – Test for vibration and backlight
9. *#*#2664#*#* – Test for touch screen
10. *#*#1111#*#* – FTA software version (in 1234 within the same code will provide a view of the PDA and firmware version)
11. *#12580*369# – Information about the software and hardware
12. *#9090# – Diagnostic information
13. *#9900# –System dump mode
14. *#301279# – HSDPA / HSUPA Control Menu
15. *#7465625# – Look at the status of phone locks
16. *#*#7780#*#* –Resetting data to default settings
17. *2767*3855# – Formatting the device to default settings (warning – this deletes all date on the devices)
18. *#*#7594#*#* – After entering this code, your device will turn off
19. *#*#232338#*#* – Display Wi-Fi MAC address
20. *#*#1472365#*#* – Quick GPS test
21. *#*#1575#*#* – Extensive GPS test
22. *#*#0*#*#* – Test LCD screen
23. *#*#0289#*#* – Audio test
24. *#*#0588#*#* – Test proximity sensor
25. *#*#3264#*#* – Display RAM version
26. *#*#232331#*#* – Bluetooth test
27. *#*#232337#*# – Bluetooth address
28. *#*#7262626#*#* – Field test
29. *#*#8255#*#* – Tracking Google Talk service
30. * # * # 3424 # * # * – test function for HTC devices
Have fun and use at your own risk. Hope these can help you out.