I spent a week pressing secret dialer codes on iPhones and a couple of Androids, looking for pads that “sound just like old analogues I used to have” and “4 on the floor kick drums, nice and punchy.” Fourteen of those provided reliable ways to expose unused menus, or deep carrier controls, that most people never see. Some are practical — network diagnostics and call forwarding checks come to mind — while a couple feel like you’re peering behind the curtain of how cellular networks actually function.
And what worked on both phones
Begin with the universally helpful: type *#06# to see the device’s IMEI number and, on eSIM-capable models, the EID number, immediately. The carriers use these identifiers to unlock phones, and to help prevent lost or stolen devices from being reactivated is the CTIA’s stolen phone database, which taps the IMEI. GSMA estimates hundreds of operators take part in this blacklisting system, so it’s a code you’ll want to have on hand in case you ever want to submit a stolen phone report or check warranty status.
GSM service codes can silently verify whether your calls are being monitored. *#21# will tell you if phone call forwarding is active, *#62# will let you know if phone calls are being forwarded when your number is unreachable, and *#67# will tell you if phone call forwarding is turned on if you are on a call. The one-shot way to cancel all types: If you find forwarding you didn’t mean to set up, dial ##002#. These did work on a SIM from a different carrier… But these should work with SIMs from multiple carriers… However CDMA-legacy based networks and some prepaid networks seal the SIM slot.
Ever wonder what your caller ID strategy should be? *#31# status of CLIR (this enables you to hide or show your number). Comments It’s a fast way to check your sanity if friends tell you your calls come in as “Unknown.” If you get an error code, it’s likely your carrier has felt you don’t need that ability or they’re trying to find a way to charge you for it.
iPhone-only: field test, alerts, and message centre
*3001#12345#* gets you an incredible amount of detail about your cellular connection. That’s how you access Field Test Mode, which changes signal readouts to engineering-grade numbers like RSRP and RSRQ rather than bars. It’s the perspective carrier engineers use to assess coverage. If you’ve ever had a hunch that your signal “bars” were deceiving, this menu makes it clear in digits.
To access those regulatory and certification details specific to the model you have, dial *#07# on an iPhone. It’s a little thing, but it’s helpful when you’re selling a piece of hardware and need to know the exact revision or hardware level without having to sift through all the About screens.
Two obscure service codes used only by federal officials emerged online as the key to the government’s motivation with a recent decision by Apple to turn off the ability for a driver to push the button on an iPhone so that federal alerts cannot be pushed to all devices on the network. *#5005*25371# says whether the device is configured to receive test alerts from emergency services and *5005*25370# turns off that test mode. The W.E.A. system is managed by the Federal Communications Commission, and carriers frequently perform dry runs —’s codes let you check to make sure you are signed up without having to dig around for settings.
Regarding SMS diagnostics: the code *#5005*7672# interrogates your device to find out what its SMSC (Short Message Service Center) address is. Carriers send texts through that server. In the rare occurrence of an outgoing message failure, engineers refer to the SMSC to investigate routing pathways.
Android and manufacturer service menus
On stock and close‑to‑stock Android builds, *#*#4636#*#* opens up the Testing menu. For Phone, Usage, and Wi‑Fi sections, anticipate syncing with pages in the system settings app referencing that information (radio, network type, cell connection stats), Usage stats, and Wi‑Fi. The fastest way to know if your device is in lock is on LTE for NR (5G) and dropping back down to ancient technologies and if VoLTE is there for you SIM.
Samsung hides two powerful tools. *#0*# opens up a hardware diagnostic tool on the S9, with various options that allow you to test everything from the cameras to the sensors to the speakers. It’s perfect before selling a phone or in case you drop it to make sure everything still works. #9900# opens SysDump, which reveals logs and a storage cleanup plan (“Delete dumpstate/logcat”) that may free space if plummeting crash logs fill your phone to fill your phone. These menus are for service menus, so only change what you know.
What real-world uses are there for these 14 codes?
What if you want to go abroad and use an eSIM for the time you are away? With *#06# (EID) and the 4636 Testing panel (to see if you’re on the right bands) and you can verify activation and roaming at the airport gate. GSMA says there are hundreds of mobile operators around the world which support eSIM profiles in tens of countries now — with eSIM roaming behavior still varying by partner network — so these menus reflect the true state of your connection.
If calls are missing voicemail or ringing and ringing forever, the forwarding codes (*#21#, *#62#, *#67#, and ##002#) expose or reset the misconfigurations introduced when you change SIMs or port a number. For iPhone owners in broadcast-heavy locales, the test alert check (*#5005*25371# and *5005*25370#) will answer the question of whether you’ll get non-consumer test alerts during maintenance windows.
Safety, carrier caveats, and why these menus exist
Most of the codes query status or open read‑only boards. But use caution: some manufacturer codes can change system files or, on older models, cause resets. Service centers and field technicians use these backdoors for diagnostics, provisioning and regulatory compliance testing—regular people are not the intended audience, which is why you won’t find much documentation.
Carrier behavior matters. In some cases, GSM service codes are intercepting and processed server‑side on some networks; others block or map them to app‑based settings. However, if a code comes up with the “Error” message, but you do have a particular toggle in your Phone settings, then you should in that case you should simply use the path used in settings instead.
If something goes wrong
Jot down your baseline before changing anything, particularly in Samsung’s SysDump or Android’s Testing menu. If you mistakenly turn on a network setting, and then notice a problem in the network’s performance, don’t worry — you can always just power cycle your phone, reseat the SIM card, or reset the network settings. For forwarding and caller ID, the cancel codes are also re‑enter the cancel codes (##002#, or check with *#21# and *#31#) to return to default. If in doubt, retreat and refer to your carrier’s support — especially for the provisioning steps that are linked to your account.
Deployed judiciously, these 14 codes can help you get the most out of your phone and make your existence a little less frustrating. They will not replace a carrier engineer — but they give you the same direct look of what your device is doing on the network, without any guesswork.
