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iPhones are known for their intuitive nature, but did you know there are a bunch of secret ‘interrogation codes’ you can dial into the Phone app to access unique diagnostic abilities that you wouldn’t ordinarily be able to access in iOS?

These codes – most of which actually predate the iPhone itself – query your carrier via your SIM card, so they won’t work if you use a digital SIM or an iPad or iPod touch without cellular capabilities.

Here, then, is a brief rundown of some of the key interrogation codes that work on an iPhone.

Field Test mode

This is one of the most useful interrogation codes on iOS, to the point where we’ve previously devoted an entire article to it. Field Test mode provides a highly technical breakdown of your iPhone’s connection to your mobile network.

To enter Field Test mode, open the Phone app and dial *3001#12345#* on the keypad.

Find out about call forwarding

Want to find out if your phone is set up to forward calls to another number? This can can be aa considerable security concern for some people. Dial these codes to bring up a readout of whether and where your phone forwards to another number under various circumstances:

  • To check Call Forwarding when a call goes unanswered, dial *#61#
  • To check Call Forwarding when you’re unreachable, dial *#62#
  • To check Call Forwarding when the call is busy or rejected, dial *#67#
  • To check if anything is being forwarded at all (calls, texts, SMS etc.), dial *#21#

Check if call waiting is set up

You can manage call waiting – the process of notifying you that someone else is calling whilst being on another call – through Settings > Phone > Call Waiting, but it’s also possible to check with an interrogation code.

To check if call waiting is set up on your phone, dial *#43#. Then, you can dial *43# to enable call waiting, or #43# to disable call waiting.

Check if caller ID is set-up

Again, it’s possible to set up Caller ID through iOS by going to Settings > Phone > Show My Caller ID. However, you can also check if Caller ID is active on your iPhone by dialling *#31#

There’s a genuinely useful spin-off from this, in that if you dial #31# immediately before a phone number, your call will be anonymous for that specific call, meaning you don’t have to go in and flick any toggles on or off.

Check your IMEI

This one isn’t as useful as it used to be, as you can now find your phone’s IMEI through iOS by going to Settings > General > About.

However, it’s good to know that you can also obtain your phone’s IMEI (useful for unlocking a carrier-specific phone and tracking stolen phones) by dialling *#06#

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