Banks often confirm transactions by phone or voice verification codes. Call Forwarding Signal lets a bank first check whether call forwarding is set up for a phone number, to confirm that the call will reach the customer.
The bank's call goes directly to the customer's phone.
Incoming calls ring normally and go to voicemail only when the line is busy or the call is unanswered.
All incoming calls are forwarded to another number.
A and BNeither has unconditional forwarding enabled, so the bank's call reaches the customer's phone first.
CUnconditional forwarding is enabled. The bank can use another way to confirm the transaction.
Call Forwarding Signal: How it works
- Forwarding settingsThe customer's call forwarding settings are stored in the operator network.
- QueryThe service provider sends the phone number to check whether unconditional forwarding is enabled or list the forwarding types currently active.
- ResponseThe operator returns active (true/false) or a list of forwarding types.
Call Forwarding Signal: API spec
POST /unconditional-call-forwardings to check whether unconditional forwarding is enabled; POST /call-forwardings to list active forwarding typesphoneNumber| Response details | Meaning | Example |
|---|---|---|
| active | Whether unconditional forwarding is enabled | true |
| inactive | Forwarding type: no forwarding set up | |
| unconditional | Forwarding type: forward all incoming calls | |
| conditional_busy | Forwarding type: forward when busy | |
| conditional_not_reachable | Forwarding type: forward when unreachable | |
| conditional_no_answer | Forwarding type: forward when unanswered |
Responses for three scenarios (excerpts)
falseUnconditional forwarding is not enabled["inactive"]No call forwarding set upfalseUnconditional forwarding is not enabled["conditional_busy", "conditional_no_answer"]Forward only when busy or unansweredtrueUnconditional forwarding is enabled["unconditional"]All incoming calls are forwardedSpec source: CAMARA CallForwardingSignal r3.3 (Call Forwarding Signal v0.4.0)
Call Forwarding Signal: GSMA use cases
Account Takeover Protection
Problem to solveBanks detect fraud during mobile authentication to prevent account takeover.
Call Forwarding Signal's roleChecks for unusual changes in call forwarding settings.
Used together: SIM Swap
GSMA source ↗GSMA case studies (1)
Sources: GSMA Open Gateway Use Case Library and API Descriptions (accessed 2026-10-14). Descriptions are summaries.