What it is #
A SIP trunk is the raw telephony connection between Voice Nimble and a carrier. Most merchants never touch this screen — the Phone Provider UI configures it automatically. Use the SIP Trunk screen only when:
- Your carrier isn't in the preset list (Twilio / Sarkar / FreePBX)
- You need multiple trunks with different failover priorities
- You're debugging a raw SIP issue
When you need a custom SIP trunk #
- You have a carrier like Bandwidth, Vonage Business, or a regional telecom that's not in the preset list
- You want a different caller-ID per outbound campaign
- You're running redundancy: primary + backup trunk
Required fields #
| Field | Example | Notes |
|---|---|---|
| Trunk name | bandwidth_primary | Just a label |
| SIP server address | sip.bandwidth.com | Host or IP |
| Port | 5060 | UDP default; TLS usually 5061 |
| Username | bw_user_42 | From carrier |
| Password | ••••••••• | From carrier |
| Caller ID number | +14155550123 | E.164 only |
Setting a default trunk #
- Mark one trunk as default — used when a broadcast or event config doesn't specify one
- You can only have one default at a time
Activating / deactivating trunks #
- Active trunks can place calls
- Inactive trunks are kept (settings preserved) but won't route traffic
Toggle on the SIP Trunk page.
Tips & best practices #
- Name trunks descriptively:
bandwidth_us_primarynottrunk1 - Use TLS port
5061if your carrier supports it — encrypts SIP signaling - Keep two trunks active with different carriers — if one fails, you can flip in seconds
Troubleshooting #
| Problem | Fix |
|---|---|
| All calls fail through this trunk | Credentials or IP allowlist — check carrier dashboard |
| Some calls fail | Carrier concurrency limit reached; talk to carrier |
| Caller ID not showing | Carrier may override — ask them to enable "CNAM passthrough" |