iphone hidden features and settings
There's a host of secret settings and features hidden on an iPhone, and here's how to get to them. iStock

A list of secret Apple iPhone codes that can unlock a raft of hidden features and settings has been revealed, allowing users to do anything from enhancing their call quality to checking their mobile balance.

While Android is particularly well known for offering a rabbit-hole of an operating system that can be tweaked and tinkered with, Apple's iOS has kept menus and settings relatively simple and locked down. However, there is a way that users can drill down to find some gems not seen on the surface.

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If you want to find out how many minutes you have left on your phone tariff, what your IMEI number (something you'll need if you swap phone networks) or even find out a way to enhance your iPhone's voice quality there's a way to do it that you won't find by going to your normal phone's settings.

Redmond Pie revealed a full list of the codes and how to use them. By typing in the following secret USSD codes on the dialpad of the phone then pressing the call button you can bring up these tricks:

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*3001#12345#*: Field Test mode

*#5005*7672#: SMS centre number

*3370#: Turn on or off EFR (Enhanced Full Rate), a mode that improves your iPhone's call quality

*#06#: Find out your iPhone's IMEI number

*#31#: Hide your number on calls option

*#43#: Check if call waiting is on or off

*43#: Turn on call waiting

#43#: Turn off call waiting

*646#: Check minutes left on contract

*225#: Find out your current mobile account balance

*777#: Find out prepaid account balance

*#61#: Number of missed calls

*#21#: Call forwarding status

*#67#: Call forwarding number

*#33#: Find out what mobile services are disabled on your phone

One of the most interesting of the USSD codes is the Field Test mode, which allows users to see their phone-signal strength measured in numbers rather than those five bars. You'll see something displaying such as '-90', with the number going up and down depending on signal. A value above -80 is a full-bar strength, but anything below -110 is very weak. This is a more accurate way of seeing whether you have enough signal to make a call, rather than holding on to hope with one-bar.

It's worth noting that you should only use these codes and play around with your settings at your own risk, if you're not sure what something does better leave it be.

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