There's no official iPhone code *#12345. You might be confusing it with the well‑known Field Test mode code: *3001#12345#*. Punch that into the Phone app and hit call to open a hidden engineering dashboard. Apple doesn’t advertise it, but it’s been around for years. Once inside, you’ll see technical cellular data that most people never touch—things like your exact signal strength in dBm (‑40 to ‑80 means excellent; below ‑110 and you’ll struggle to hold a call), which cell tower you’re connected to, network band info, and SIM‑related diagnostics. For the average user, the most practical takeaway is turning those vague signal bars into an accurate numeric readout. On older iPhones with a Home button, you can force that number to stay in the status bar by holding the power button until the shutdown slider appears, then holding the Home button until you jump back to the home screen. On Face ID models, that trick no longer works—the display reverts to bars once you exit. If you tap around inside Field Test, don’t worry: you won’t break anything, but most of the settings are carrier‑level parameters that you shouldn’t mess with unless you know what you’re doing.

If you actually want a code that does something useful without diving into engineering menus, skip the guesswork. *#06# instantly shows your iPhone’s IMEI number—the unique ID you need for warranty claims, carrier unlocks, or filing a theft report. *#67# checks where your calls go when you’re busy, and *#21# shows whether unconditional call forwarding is active. Carriers also have their own codes: AT&T users can dial *3282# to check data usage, Verizon uses #3282, and T‑Mobile uses #932#. The bottom line: *#12345 does nothing. Stick with the real codes above, and you’ll actually get somewhere.