Call Forwarding (CF) in the UK is subject to strict regulatory controls regarding Caller Line Identification (CLI). When a call is forwarded, the system is designed to present the original incoming number to the recipient to maintain transparency and prevent fraud. However, this creates a conflict when you wish to enforce a specific outbound CID for business purposes.

Why Extension Enforced CID Takes Precedence

In standard configurations, the "Extension Enforced CID" setting on the forwarding extension always takes precedence over outbound route overrides. This occurs because the call forwarding action is treated as an internal transfer or redirection within the PBX logic before it hits the outbound gateway. Consequently:

• Outbound route CID overrides are ignored because the call is already associated with the originating extension’s identity.
• The system prioritises the extension’s configured CID to ensure the forwarded call appears to come from the employee, not the original caller.

The Solution: Forcing a Single Outbound CID

To force a single, specific outbound CID for all forwarded calls, you must bypass the standard extension enforcement by creating a distinct call path. This requires a two-step configuration:

1. Create a New Outbound Route:

• Set up a dedicated outbound route specifically for forwarded calls.
• Assign a unique prefix (e.g., 99) to this route.
• Configure the dial pattern to match calls requiring this specific CID handling.

1. Create a New Trunk with CID Override:

• Provision a new SIP trunk or configure an existing one specifically for this route.
• Enable the CID Override setting on this trunk.
• Set the desired outbound CID (e.g., your main business number).

When a call is forwarded using the unique prefix, it will route through this new trunk, where the trunk-level CID override will take precedence over the extension settings, ensuring the correct number is presented.

Modern Alternative: SIP Clients

It is worth noting that this complex configuration is rarely needed in modern environments. Many users now utilise SIP clients such as Groundwire or similar mobile-switch applications. These clients offer a far more feature-rich experience, allowing users to:

• Manage calls directly from their mobile device.
• View and display the incoming caller’s CID clearly on the screen.
• Handle forwarding natively without requiring PBX-level CID manipulation.

If you are experiencing issues with CID presentation, consider whether migrating to a robust SIP client solution would better meet your needs than configuring complex outbound routes.