Call forwarding: every code, what it does, and how to turn it off

Call forwarding is one of the oldest features on a phone network and still one of the most misunderstood, because there are really four separate features wearing one name. Get the distinction and every confusing message the network sends you starts making sense.

The four kinds of forwarding

Include the number in full international format where you can (**21*+15551234567#) because a national-format number sometimes fails silently when you are roaming.

Unconditional vs conditional, and why it matters

Unconditional forwarding means the network diverts the call before your handset is ever involved. Your phone does not ring, no missed-call notification appears, and to you it looks as though nobody called. That invisibility is the feature, and it is also why unconditional forwarding is the mechanism behind a well-known family of account-takeover attacks. If calls and verification codes suddenly stop arriving, dial *#21# before you assume the network is broken.

Conditional forwarding leaves your phone in the loop. It rings, and only if the condition is met does the call move on. This is what voicemail is built on: your carrier sets conditional forwarding to the voicemail platform when the line is activated. Which explains a question people ask constantly: why cancelling all forwarding also kills your voicemail.

Decoding “call forwarding unconditional - voice not forwarded”

This message means the network accepted your instruction for some services but declined it for voice specifically. The usual causes, in rough order of likelihood:

1. The feature is not provisioned on your line. Many prepaid plans and some business plans exclude call forwarding entirely.
2. The destination is not permitted. International or premium-rate targets are commonly blocked because the line owner pays for the forwarded leg.
3. The number format was rejected. Try full international format with the plus.
4. An unpaid balance or account hold is suppressing chargeable features.

It is not a phone fault, and factory-resetting the handset will not change it. The setting lives in the network, not on the device.

Turning forwarding off properly

Carrier apps and settings menus

Every major carrier also exposes forwarding in its account app and in the phone's own settings, and those are easier when they work. Two caveats worth knowing.

• iPhone's Settings → Phone → Call Forwarding only controls unconditional forwarding. Conditional rules set at the network level are invisible there, which is why the toggle can read “off” while calls still divert.
• Android varies by manufacturer and carrier. The USSD codes work identically across all of them, which is why they remain the reliable answer.

Where a carrier documents its own codes, we have written them up one carrier at a time — start with the Verizon call forwarding guide, or the rest of the call forwarding guides.

What businesses should use instead

Handset-level forwarding is a blunt instrument for a business line. It forwards to exactly one destination, it gives you no record of what happened, and it fails silently when the destination is busy.

A cloud phone system replaces it with routing you can actually reason about: ring several people at once or in sequence, fall back by time of day, send overflow to a queue with hold music, and record every leg. Anything unanswered can go to an AI receptionist that takes the message, answers the routine question, or books the appointment, rather than to a voicemail box nobody empties.

The practical difference: forwarding moves a problem to another phone, routing resolves it. And because every step is logged, you can finally answer the question forwarding never could: how many calls did we actually miss?

Forwarding on landlines and VoIP lines

The star codes above are GSM mobile codes. Landlines and VoIP lines use their own conventions, and mixing them up is why a code copied from a mobile guide silently does nothing on an office phone.

The distinction matters more than it looks. On a mobile or a landline, forwarding is a property of the *line*. On a cloud platform it is a property of the *routing rule*, which means it can depend on the time of day, who is available, which number was dialled, and what happened on the previous attempt, none of which a star code can express.

The security angle nobody mentions

Unconditional forwarding is silent by design, and that is precisely what makes it useful to an attacker. Someone who gains brief access to your handset, or who social-engineers your carrier, can set forwarding on your line and receive every call and voice-delivered verification code you would otherwise get, while your phone shows nothing at all.

• Check periodically. Dial *#21# and *#004# occasionally, particularly after a phone repair, a SIM swap, or any carrier account change you did not initiate.
• Treat sudden silence as a symptom. If calls stop arriving and you assumed a quiet week, check forwarding before you blame the network.
• Lock the carrier account. A port-out PIN or account password stops the social-engineering route, which is the more common attack of the two.
• Watch for unexpected charges. Forwarded legs are billed to you, so an international forwarding destination shows up on the bill before anything else does.

For a business line the same risk applies with more consequence, because the forwarded calls are customers. On a cloud platform this is one of the quieter arguments for routing over forwarding: every routing change is logged against a named user, so an unexpected one is visible in an audit trail rather than invisible in the network.