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Glossary · Voice technology

What is Conditional call forwarding?

  • Also called: conditional forwarding, forward on no answer, forward on busy

Reviewed by Sujan ThapaliyaLast updated

Definition

Conditional call forwarding moves a call to another number only when a condition is met: you did not answer, the line was busy, or the phone was unreachable. The handset rings first, which is why the rule is easy to set and easy to forget.
The three STIR/SHAKEN attestation levels, which underpin how conditional call forwarding behaves in practice: A asserts both that the carrier knows the customer and that the customer may use the calling number, B asserts the customer only, and C asserts neither. A shared number pool can reach B at best, which is why number ownership keeps recurring in these definitions.
Attestation is the backdrop to most caller-ID and deliverability terms, conditional call forwarding included.

In practice

How conditional call forwarding actually works

Voicemail itself is usually implemented as conditional forwarding to the mailbox, which is why clearing all forwarding rules can quietly disable voicemail as well.

Because the phone still behaves normally, a stale conditional rule can survive for years, sending unanswered calls to a number nobody uses. The symptom is callers reporting they left messages you never received.

Unconditional forwarding is the opposite: the handset never rings at all. The two are set with different codes and cleared with the same one.

Conditional rules are also invisible in most handset settings screens, which show unconditional forwarding only. That is why the reliable way to audit them is the network interrogation code rather than the phone's own menu, and why clearing everything and setting only what you want is often faster than diagnosing what is there.

Worked example

A no-answer rule set once during an office move can survive for years. The symptom is customers insisting they left messages you never received, on a phone that rings normally.

Conditional call forwarding: common questions

What is conditional call forwarding?
Forwarding that applies only under a condition — no answer, busy, or unreachable. Your phone rings first, and the call moves only if that condition is met.
How do I check whether conditional forwarding is set?
Query the rules from the handset with the interrogation code for your network, or clear all forwarding and set only what you want. The status will not appear in the phone's own settings screen, which typically shows unconditional rules only.
Does clearing forwarding disable my voicemail?
It can. On many networks voicemail is a conditional forward to the mailbox, so clearing every rule at once removes it too. Re-enable voicemail after a full reset.

Sources

  1. Combating Spoofed Robocalls with Caller ID Authentication — Federal Communications CommissionThe STIR/SHAKEN framework, the attestation levels carriers sign calls with, and the mandate requiring providers to authenticate caller ID.
  2. 47 U.S.C. § 227 — Restrictions on the use of telephone equipment — Cornell Legal Information InstituteThe Telephone Consumer Protection Act itself — the consent requirements, calling-hours limits, and private right of action.
  3. ITU-T Recommendation E.164 — The international public telecommunication numbering plan — International Telecommunication UnionThe international number format, the 15-digit maximum, and how country codes and national numbers compose.

See conditional call forwarding in the product

An IVR (interactive voice response) system answers inbound calls and routes them using a menu, a spoken request, or data it already holds about the caller. Good IVR gets someone to the right person in one step. Bad IVR is the reason people press 0 repeatedly.

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