The iPhone is one of the most impressive tool with several excellent features though there are many hidden features as well as tricks which one may have not realised that existed till now. Some of these features seem to be buried in the Settings menu while there are others that are hidden in plain sight
Dialling 3001#12345# and then pressing the call button. Your phone will switch away onto a grey screen, after which you’ll see the extra information. One of the most useful features is a more detailed signal strength indicator which should appear in the top-left hand corner.
There are some other codes that offer some more informative.
Using #33# will show the status of your call barring settings. It can be turned on and off using 33*pin# and #33&pin#. Swap PIN for your Sim PIN.
Using *#43# will tell you call waiting is turned on or not. That feature allows people to queue up when they ring you, so that the phone can alert you if someone is trying to get through while you’re already on a call.
You also turned on using *43# and turned off again with #43#