Your iPhone’s Phone app keypad doubles as a terminal into the GSM network stack. Dial the right sequence and hit call, and you’re not “calling” anyone. You’re sending a Supplementary Service (SS) or USSD request straight to your carrier’s switch, or triggering a manufacturer diagnostic mode on the device itself.
None of this is an Apple feature. These are decades-old GSM/3GPP standards that happen to work on any phone, iPhone included, because the codes get intercepted by the baseband before a normal call is placed. Support and exact behavior still vary by carrier, so treat every result below as “should work on AT&T, T-Mobile, and Verizon” rather than guaranteed.
Device Info
| Code | What It Does |
|---|---|
| *#06# | Displays the IMEI (and MEID/serial on some models). No call is placed; the number just appears on screen. Useful for insurance claims, warranty checks, and confirming a used iPhone isn’t reported lost or stolen. |
| *#07# | Opens the device’s regulatory and certification information (SAR values, compliance markings). |
Call Forwarding
Call forwarding on iPhone is normally a Settings toggle, but the underlying codes let you check or set it directly, which matters if you’re troubleshooting a line that seems to be forwarding calls without an obvious setting change.
| Code | What It Does |
|---|---|
| *#21# | Checks the status of unconditional call forwarding: is it on, and if so, to what number. |
| *#61# | Checks the forwarding destination for calls you don’t answer. |
| *#62# | Checks the forwarding destination used when your phone is off or out of coverage. |
| *#67# | Checks the forwarding destination used when your line is busy. |
| ##002# | Cancels every type of call forwarding at once. This is the fastest way to be sure nothing is being redirected. |
| **21*[number]# | Turns on unconditional forwarding to the number you enter. |
| ##21# | Turns off unconditional forwarding. |
Call Waiting, Call Barring, and Caller ID
| Code | What It Does |
|---|---|
| *#43# | Checks whether call waiting is currently enabled. |
| *43# / #43# | Turns call waiting on or off. |
| *#33# | Checks the status of call barring (blocking outgoing or incoming call classes). |
| *33*[PIN]# / #33*[PIN]# | Enables or disables call barring using your barring PIN. |
| *#31# | Checks whether your outgoing caller ID is being shown or hidden on calls you place. |
Network Diagnostics
| Code | What It Does |
|---|---|
| *3001#12345#* | Launches Field Test Mode, which replaces the signal bars with the actual signal strength in dBm. A reading closer to 0 (for example, -60) is a strong signal; a reading further from 0 (for example, -110) is weak. This is the same underlying data Apple used to expose via a secret bars-to-dBm tap sequence in older iOS versions. |
The Spyware Myth
A claim that resurfaces constantly online: dialing *#21#, *#61#, *#62#, or *#67# will “reveal if your phone is tapped.” It won’t. These codes report the state of a legitimate carrier feature, call forwarding, not the presence of surveillance software or a wiretap. If one of these codes returns a number, in the vast majority of cases that number is your own carrier’s voicemail platform, returned because forwarding-to-voicemail is how “unanswered” and “unreachable” call handling is implemented on the network side. Seeing a number there is normal, not a red flag.
Actual mobile spyware runs as an app or a malicious profile, and it doesn’t announce itself through call-forwarding status. If you suspect a compromised device, the useful checks are Settings > General > VPN & Device Management for unrecognized configuration profiles, Settings > General > iPhone Storage for unfamiliar apps, and a review of Screen Time / battery usage for anything with outsized background activity, not a dialer code.
Quick Reference
Bottom Line
These codes are a fast, no-app way to audit call handling on a line, confirm an IMEI, or get a real signal-strength number instead of a bar graph. They are not a backdoor, and they are not a spyware detector. Know what each one actually queries, and they’re a genuinely useful five seconds on the keypad.
