They are accessed 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 a sequence of numbers in between (there's close-to-zero chance that anyone would accidentally access them).
These publicly available backchannels allow users to directly communicate with their service provider's computers and/or access back-end features in their device. But there is some trickiness you'll need to know about.Ĭoders have a storied tradition of baking in secret passageways that can only be accessed by inputting a special 'key.' And so that tradition continues in the mobile age. The USSD protocol allows you to access hidden features you didn't know about right from your smartphone's dialer. This protocol was originally created for GSM phones, but can be found on CDMA devices as well (if that's a bunch of acronym gibberish to you, here's a quick primer). Unstructured Supplementary Service Data (USSD), sometimes known as 'quick codes' or 'feature codes', is an extra-UI protocol, which allows people to access hidden features.
