PBX Not Receiving Calls
Outbound calls work fine but nothing is coming in — that points to routing, not your PBX itself.
When a PBX can make outbound calls normally but stops receiving inbound calls, the issue is usually in how calls are routed to it — either at the carrier, the trunk, or the DID assignment — rather than the PBX hardware itself.
Likely causes
Ranked from most to least common based on what we see in the field.
- DID routing or carrier port issue misdirecting inbound calls
- SIP trunk registration expired or failed
- ISP or carrier outage affecting inbound service only
- Firewall blocking inbound SIP INVITE requests
- MAC/programming change altered call routing rules
- Failed trunk card on a legacy PBX
- Auto-attendant or IVR misconfiguration silently dropping calls
What you can check first
Safe steps that take a few minutes and can save a truck roll.
- Confirm outbound calls still work normally — this narrows the fault to inbound routing
- Have a colleague call your main number from a cell phone and note what happens (ringing, straight to voicemail, busy, silence)
- Check your carrier's portal for any recent number or routing changes
- Confirm the SIP trunk shows as registered/connected in your PBX admin panel
- Check the carrier's status page for reported outages
How we diagnose it
We check trunk registration status first, then trace how the carrier is routing your DIDs, then inspect firewall rules for blocked inbound SIP traffic. A test call with live packet capture usually shows exactly where the call is being dropped.
Fixing it
Depending on the cause, we correct DID routing with your carrier, fix firewall rules blocking inbound SIP, repair or re-register the trunk, or replace failed hardware on legacy systems.
- Carrier-side DID routing correction
- Firewall rule audit for inbound SIP traffic
- SIP trunk re-registration and testing
- Legacy trunk/station card diagnosis and replacement
Frequently asked
Why do outbound calls work but not inbound?+
Outbound and inbound calls can use different paths through your carrier and firewall. A routing or firewall rule affecting only inbound traffic will produce exactly this symptom.
Could this be a problem with our phone number itself?+
Yes — a DID that's been misrouted or improperly ported can cause calls to fail before they ever reach your PBX. We coordinate with your carrier to check this.
Do callers get an error, or does it just ring forever?+
It varies — callers may hear ringing with no answer, get a busy signal, or reach a fast disconnect, depending on where in the path the call is failing.
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