Entering *#06#into your iPhone's dialer and pressing the green call button will display your device's unique identification number, known as the IMEI, along with your EID -- a unique 32-digit serial number found on devices that support eSIM technology. If you have a dual SIM or eSIM phone, you'll see more than one IMEI listed. This number is often needed when reporting a stolen phone, checking warranty status, or unlocking your device for use on another carrier.

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Tip:On an iPhone, you can also find the IMEI under Settings > General > About, but using the code is faster.

Type *3001#12345#* to open the "FTM Dashboard" (Field Test Mode Dashboard) -- a hidden engineering menu that displays your carrier, capabilities, phone number, cell tower IDs, network bands, andyour signal strength measured in dBm instead of bars. You'll also see other information listed in this menu, although much of it is jargon only technicians would understand.

OK, while the code above is for iPhone users, this one is for Android users. It opens a technical menu with phone status, LTE/5G info, Wi-Fi details, app usage stats, and battery history. It's mainly intended for technicians diagnosing connectivity issues or checking detailed system health. Most people probably won't understand it.

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Some carriers let you dial these codes to see if call forwarding is enabled and which number your phone is currently forwarding calls to -- either when you're busy (*#67#) or for all calls (*#21#). You can change it to forward calls to another number, such as your home, office, or a third-party answering service, in settings.

On iPhone, to change the forwarding number, go to Settings > Phone > Call Forwarding. On Android, the steps vary, but generally you'll open the Phone app, tap the three-dot menu, go to Settings > Calling accounts, select your active SIM, and then look for the call forwarding option.

If you see "Failed/Error" instead of "Enabled/Disabled" displayed after entering these codes -- and you don't see call forwarding in your settings -- it likely means your carrier doesn't support the feature on your plan.

Similar to the call forwarding menu above, dialing *#43#lets you check whether call waiting is enabled -- the feature that alerts you to another incoming call while you're already on one.

To enable call waiting on an iPhone, go to Settings > Phone > Call Waiting and toggle the switch on. On an Android phone, you typically open the Phone app, then go to Settings > Calls > Supplementary Services > Call Waiting and toggle it on, though the steps may vary by device.

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If you enter the code and see "Failed/Error" instead of "Enabled/Disabled" -- and you can't find a call waiting option in your phone's settings -- your carrier likely doesn't support this feature on your plan.

Call forwarding is useful if you're traveling, using a different phone temporarily, or want all calls sent to a work or home line instead of your mobile. With this code, it's easy to forward all incoming calls to another number -- just enter *21[number]#into your dialer. (The number that's in brackets will be the destination for your calls.) As mentioned earlier, you can also enable or disable call forwarding in settings if your carrier and plan support it.

Checking your bill balance is quick and easy with these codes. They work right from your dialer, so you don't have to log in to an app or website to see what you owe. On Verizon, dial#225 to get a text message with your current balance. AT&T customers can dial *225#for the same information, while T-Mobile users can dial#225#.

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If you want to keep tabs on your data usage, each major carrier has its own code. Verizon customers can dial#3282, AT&T users can dial *3282#, and T-Mobile customers can dial#932#. You'll get a text showing how much data you've used and, in most cases, when the cycle resets -- great for avoiding overage charges or throttling.

Need to pay your phone bill? Verizon makes it easy with the code#768. To make a payment over the phone with T-Mobile, you can use the code *729. 

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Your iPhone can receive emergency, government, and public safety alerts, including AMBER alerts, extreme weather warnings, and imminent threat notifications. By default, these are turned on, and you'll hear a loud, alarm-like sound when one arrives. You can enable or disable them anytime by going to Settings > Notifications and toggling the alert types under Government Alerts.

You can also dial *5005*25371#to check if your phone is set to receive test alerts from government and emergency services. This code doesn't trigger a real alert -- it simply returns a yes or no to confirm whether the feature is enabled. If it's on and you'd rather disable it without going into settings, dial *5005*25370#and press the call button to turn it off.

Want to see your phone's compliance and safety information? Dial *#07#to quickly access warranty info, FCC details, and RF exposure guidelines. It's essentially a scrolling page of legal text.

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In the US, dialing *67 before a phone number hides your caller ID for that one call, making "Private Number" appear on the recipient's screen, which is useful when calling businesses or people you don't know well. Outside the US, the equivalent code is *31#, so it works the same way in regions where *67 isn't supported.

Tip:If your caller ID is normally hidden but you want it to appear just once, dial *82 before the number to temporarily unblock it.

This isn't technically a code, but it's a handy number you can dial in the US. Calling 511 connects you to your state's traffic info line, giving you real-time road updates and travel information without using data. It's useful if you don't have enough service to load GPS, or if you're close to hitting your data cap but can still make a call.

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I didn't test this code because reports say it will instantly wipe an Android phone and reinstall its original firmware -- with no warning screen. Yikes. I suggest using it only if you're selling, recycling, or fully restoring your device, as it will completely erase everything and start fresh.