MUST READ.....See Codes that unlock phone’s hidden feature

Hehe....Programmers plant secret pathways that can only be accessed by inputting a special “key.”These are the Unstructured Supplementary Service Data (USSD), “quick codes” or “feature codes,” an extra-User Interface protocol, which allows users to directly communicate with their service provider’s computers and/or access back-end or hidden features in their device. This protocol was originally created for GSM phones, but can be found on CDMA devices as well.The codes usually begin and end with the * or # keys with a sequence of numbers in between.

According to http://www.pcmag.com, these codes seldom work across different carriers, OSes, or phone models (or even on generations of the same model).If you really want to try them out, your best bet may be to Google your phone’s make and carrier + “USSD” for a tailored, comprehensive list.  Click through our slideshow for 11 codes that I can confirm worked on at least one device.
Field mode
To access field mode and get info about local networks and cell towers, dial *3001#12345#*
General test mode
The code*#0*# prompts a library of different phone operations, (e.g. Sleep, Front Cam, Vibration), which could be operated with a single push. The code mostly works with Android.
Display your IMEI
Dial *#06# to see your International Mobile Equipment Identity. The code may not work with   Verizon on an iPhone. It can work with a T-Mobile SIM. It can also work on Android AT&T device as well.The IMEI is unique to your device. Among other things, the number can help “blacklist” stolen devices or help with customer support
.Check your call forwarding:The code *#67# allows you to check which number your phone is currently forwarding calls to when you’re busy or when you reject a call.By default, this is probably your carrier’s voicemail service, but you can change it to forward to a different number (a home number, office number, or third-party answering service for example).To change the number on  iPhone, go  to Settings > Phone > Call Forwarding. On Android (varies from system to system), tap the Phone app > hamburger icon > Settings > Call > More Settings > Call forwarding.
Hide your phone from caller ID
Entering code #31# will prompt a pop-up stating that your Caller ID had been disabled. In order to re-instate Caller ID, enter *31#. The code can only work on Android.
SMS message centre
The code*5005*7672# will tell you your SMS message centre number.
Activate call waiting
The code*43# will activate call waiting; you can deactivate it by entering #43#.
Stop receiving calls, or put your phone on SMS mode
Dial *35*0000*11#send.Dial #35*0000*11#send to cancel it
Stop receiving SMS on your phone
Dial *35*0000*16#send.Dial #35*0000*16#send to cancel it