Unstructured Supplementary Service Data (USSD) sometimes known as “quick codes” or “feature codes” is an extra-UI protocol, which allows people to use hidden features. This protocol is for GSM phones, but it’s usable on CDMA devices as well.
These publicly available back-channels allow users to directly communicate with their service provider’s computers and/or access back-end features on their device. You can execute the code by inputting them into the phone’s dialer (the screen you use to start a phone call) and usually begin and end with the * or # keys with numbers in between (there’s close-to-zero chance that anyone would accidentally access them).
These quick 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, search on Google your phone’s make and carrier + “USSD” for a tailored, comprehensive list.
The Quick Codes can Include:
Display your IMEI: *#06#
To see your phone’s IMEI, type in the above code, and then the green call button to prompt your IMEI number (or your International Mobile Station Equipment Identity Number). 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: *#67#
This code allows you to check which number your phone is currently forwarding calls to when you’re busy or 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). On an iPhone, you can change this number by going to Settings > Phone > Call Forwarding. On Android (varies from system to system), tap the Phone app > hamburger icon > Settings > Call > More Settings > Call forwarding.
Get Even More Info on Call Forwarding: *#61#
On my Galaxy phone, this code prompted a pop-up that let me know how long until a call is forwarded to the message center. On the iPhone, regardless of carrier, this code just showed me the same info as *#67#.
Quick Test Menu (Samsung Galaxy Only): *#7353#
This code only works on Samsung Galaxy models. This brings up a menu with a number of one-tap test prompts. The first test is “Melody,” which prompts a jaunty little K-Pop diddy. I don’t know who the artist is (it’s un-Shazammable!), but a search of the lyrics pointed me to this YouTube clip, with a title that translates to “Samsung Any call Galaxy basic level – Hey Now (Goodbye).” If you have any details on this mobile mystery, drop it in the comments.
Firmware (Samsung Galaxy Only): *#1234#
Once again, as far as I can tell, this only works on Galaxy devices. But it will let you know your phone’s current firmware. So, have fun with that.
Display Software Version date month & year: *#0000#
This works only on Java mobile devices and older mobile phone brands. It displays the software version, manufacture date and default language of the device. Here, you can change the purchase date here and it stores repair dates (if any repair has been done).
Regulate Voltage and Temperature: *#0228#
This brings temperature regulation on your phone. You can navigate through the available options.