Voice error: Cannot connect to number

Issue symptoms

When I place an outbound voice call, I get the Voice (formerly Talk) error: Cannot connect to number.

Resolution steps

Ensure the number uses the international format E.164. For more information, see What are the accepted phone number formats for Voice?

If the number is formatted correctly and the error persists, the callee or their external carrier might’ve blocked the number. If the individual callee blocked the number, try to call from another Voice number to find out why the end user blocked it.

External carriers use phone number reputation systems. If a number's reputation score reaches a threshold, the carrier can block it.

To resolve this, report the Voice number you use to call to the destination carrier. You can register your number at https://www.freecallerregistry.com/fcr/, that is a shared database that multiple providers use to share caller reputation.

See the table below for common carrier registries for number reputation.

Carrier | Notes | Registry

Verizon

Verizon provides a link to help mark a number as allowed. However, Verizon still passes the information to its third-party vendor.

https://voicespamfeedback.com/vsf/

https://reportarobocall.com/trf/#

Sprint | | https://reportarobocall.com/trf/#
US Cellular | | https://reportarobocall.com/trf/#
Hiya | Hiya services some major carriers and numbers outside the United States. | https://hiya.com/manageyourcallerid
AT&T Wireless | AT&T uses the vendor Hiya. AT&T Mobility Services indicates to report the number through Customer Care Support, or by registering the number with Hiya. | https://hiya.com/manageyourcallerid

Carrier registry links

External Link Notice: The carrier registry URLs listed below are maintained by individual carriers and may change over time. These links were verified as of September 2026 but carrier websites are periodically redesigned.

If a link doesn't work:

Search for "[Carrier Name] CNAM registry" or "[Carrier Name] caller ID registration"

Visit the carrier's main website and look for the support/business services section

Contact the carrier directly for the current CNAM registration process

Carrier registry links:

AT&T

Verizon

T-Mobile

Note: Phone number reputation can take time to update. There’s no guarantee on how long it’ll take for the block to be removed. Continue to monitor the situation and report the issue to the external carrier.

Register your business and Voice numbers for Secure Telephone Identity Revisited and Signature-based Handling of Asserted information using toKENS (STIR/SHAKEN) and Calling Name (CNAM) to improve call acceptance rates. After you register for CNAM, carriers associate the number with a valid company and improve the number's reputation. To get started and see the full list of requirements to register for CNAM, see Does Zendesk support CNAM?

International Caller ID Registration

US-Centric Feature: The caller ID registration process described in this article is specific to US telephone carriers.

International considerations:

Canada: Some Canadian carriers support CNAM registration. Process varies by carrier. Not as standardized as the US system. Contact your Canadian carrier for availability.

Other Countries: Most countries outside North America do not use the CNAM system. Each country has different caller ID systems. Caller ID display depends on local telecom regulations, carrier technical capabilities, and recipient's phone/carrier settings.

If calling internationally from Zendesk Voice:

Your registered CNAM (US) typically won't display outside North America

Recipients may see: Your phone number only, "Unknown" or "Private number", Country code + number, or no caller ID at all.

Alternative for international calls:

Use local phone numbers for countries you call frequently

Recipients are more likely to recognize a local number

Some carriers have better caller ID support for local numbers

For more information on Voice errors, see What are the most common Voice error messages?