Short answer:

The phone has power but can’t reach (or authenticate with) the PBX/provisioning server. Until it can contact the server and register, calling is disabled.

Most common causes

• Network/VLAN/DHCP – Phone is on the wrong VLAN, has no IP, or didn’t get proper DHCP options (e.g., Option 66/160 if used).

• DNS/Domain – The PBX or provisioning FQDN doesn’t resolve from the phone’s network.

• Firewall/NAT – Outbound SIP/HTTPS/NTP/DNS is blocked. (Typical needs: SIP 5060/5061, RTP media range, HTTPS/HTTP to provisioning, DNS 53, NTP 123.)

• Server URL/Proxy – Wrong “Server” or “Outbound Proxy” address on the phone, or stale config pointing to an old domain.

• Time/Certificates (TLS) – Incorrect date/time causes TLS failures to the PBX or provisioning server.

• Provisioning/PBX issues – Provisioning server or PBX unreachable, account disabled, or device/MAC not allowed.

• Switch/security – Port shut, LLDP-MED/VLAN mismatch, 802.1X/NAC blocking the device.

Quick checks (2–3 minutes)

1. Home → Status → Network: Confirm the phone shows a valid IP, subnet, gateway, DNS, and expected VLAN.

2. DNS & Ping: From the phone’s Diagnostics, ping the PBX FQDN (or try browsing to the provisioning URL from a PC on the same LAN).

3. Time: If the date/time looks wrong, fix NTP or temporarily set the correct time and reboot.

4. Server/Proxy: Verify the PBX/provisioning URL exactly matches what SmartPBX expects.

5. Cable/Port swap: Try a known-good cable/port to rule out local wiring or switch config.

6. Reboot: After correcting anything above, reboot the phone to retry registration.