Linking a SIP Trunk (Bring Your Own Numbers)

Last Updated: 2026-05-25

If you already own phone numbers through another provider — a PBX, Bandwidth, Telnyx, a telco SIP trunk, RingCentral, 8x8, or anything else — you can link those numbers to Mylla instead of buying new ones. Mylla connects to your trunk over SIP, and your existing carrier keeps billing you for the numbers themselves.

This is different from buying a Mylla number — you're keeping your current provider and just pointing their traffic at Mylla.

Not sure whether SIP is the right path? Use Connect a Phone Number to Mylla to compare SIP with buying, forwarding, and porting.

When to use SIP linking

✅ You have an established business number you can't or don't want to port
✅ You have a PBX routing calls internally and want Mylla to handle specific DIDs
✅ You want to keep your current SIP provider for cost, compliance, or contract reasons
✅ You run multiple DIDs and want selective Mylla coverage per number

If you just want a new phone number and don't have an existing provider, go to Numbers and buy one directly — that's much simpler.

Before you start

You'll need:

Admin access to your current SIP provider's dashboard (Bandwidth, Telnyx, your PBX admin, etc.)
The phone numbers you want to link, in E.164 format (+14155551234)
(Optional) SIP digest auth credentials if your provider requires them
(Optional) The source IP ranges your provider sends traffic from

Linking numbers

Go to Numbers
Click Link SIP Number in the top-right

In the side panel that opens, fill in:

Field	What to enter
SIP Trunk Name	A label for your trunk (e.g., Main PBX, Bandwidth trunk)
Phone Numbers (E.164)	The numbers you want to link, one per line. Must start with `+` and the country code
Agent (optional)	Pre-assign all imported numbers to one agent
Username / Password (optional)	SIP digest auth credentials if your provider requires them
Allowed Source IPs (optional)	CIDR ranges your provider sends traffic from (e.g., `44.234.0.0/16`). Leave empty to allow any source

Click Continue — Mylla validates the numbers and shows you which ones will import
Review the list and click Import
When import finishes, copy the SIP Hostname shown on the success screen (e.g., sip.mylla.ai)

Point your provider at Mylla

This is the step that actually routes calls. Without it, nothing changes at your provider and calls still go wherever they were going before.

On your SIP provider's dashboard:

Find the number (DID) you just imported into Mylla
Edit its outbound origination / termination route
Set the destination to the SIP Hostname from the success screen
If you entered a username/password in Mylla, configure the same digest auth on your provider
Save — calls to that number should reach Mylla within a minute or two

Per-provider quick reference

Provider	Where to set the Mylla SIP Hostname
Bandwidth	Accounts → Voice → SIP Peer → Termination Settings
Telnyx	Voice → SIP Trunks → [trunk] → Outbound → Destination
Twilio (external account)	Elastic SIP Trunking → Origination → Add Origination URI
RingCentral	Admin → Phone System → Phones & Devices → SIP Trunking
Plivo	Voice → SIP Trunks → Termination
Generic PBX (Asterisk, FreePBX, 3CX)	Add a trunk with host = Mylla SIP Hostname

Capturing caller names

Mylla automatically captures the caller's number on every SIP call. Capturing the caller's name requires one extra toggle in your PBX or carrier — see Capturing Caller Names from SIP Trunks for the per-vendor setup (3CX, FreePBX, Asterisk, RingCentral, Cisco CUCM, Bandwidth, Telnyx, and others).

If your PBX doesn't expose a name-injection toggle, calls still work normally — the agent gathers the name verbally and saves it to the customer record.

Verifying your trunk

After import, click Verify trunk on the success screen (or on the number detail page later). Mylla then waits up to 15 minutes for the first real inbound SIP call to your linked number. As soon as one arrives, the status flips to Verified and you'll get a confirmation notification.

If verification times out, place a test call from your PBX or a phone outside it. You can re-run Verify trunk as many times as you need.

What verification means: Mylla observed a test call reach the linked number. It confirms the imported number and route can deliver at least one inbound call to Mylla; it is not a full trunk-health guarantee for every future carrier route, PBX branch, codec, or failover path.

Watching SIP activity

Once a test call has been observed, every linked number's detail page helps you inspect recent SIP activity:

Last inbound — when Mylla last received a call on this number
Last failure — most recent rejection (auth, routing, or other) translated into plain English
Failure streak — consecutive failures since the last successful call (resets to zero on any successful inbound)
Recent SIP events — a short timeline of the last few connects, settings changes, auth failures, and routing problems

Mylla also sends notifications for key trunk events:

Test call observed — first successful inbound after import
Authentication failed — your PBX hit Mylla but the username, password, or source IP didn't match
Call routing failed — a SIP call reached Mylla, but Mylla couldn't route it to an agent

You can manage which channels these go to (in-app, email, push) under Settings → Notifications.

Testing

From a phone not on your PBX, dial your linked number
The Mylla agent should answer with its configured greeting
Check Calls — the call appears with source SIP
Check Numbers — your imported number shows status SIP and the detail page records a call.connected event

Troubleshooting

Symptom	Likely cause
Calls ring but go to voicemail	Your provider isn't routing to the Mylla SIP Hostname — recheck the termination config
`403 Forbidden` on your provider's logs, "Authentication failed" notification in Mylla	Digest auth mismatch or source IP not allowed — update credentials / allowed IPs in Mylla
Call connects then drops immediately	Codec mismatch — Mylla supports G.711 (PCMU / PCMA) and OPUS. Disable non-standard codecs on your trunk
"Number not found" at Mylla	The DID imported didn't match exactly what your provider sends in the `To:` header. Confirm E.164 format on both sides
Works during the day, fails at night	Some providers rotate outbound IPs — add broader CIDR ranges to Allowed Source IPs
Verification stuck in Pending for 15 minutes	No real inbound call arrived during the window. Place a call from outside your PBX and click Verify trunk again

If you're stuck, contact support with:

Your SIP trunk name in Mylla
A call SID / call ID from your provider
The approximate time of the failing call
A screenshot of the Recent SIP events panel from the number detail page

Billing

SIP-linked numbers have no monthly charge from Mylla — you're not renting the number from us. You only pay Mylla for minutes used during calls.

SIP-linked numbers also have a $0.00 phone connection charge from Mylla. After your included minutes are used, SIP calls are billed at the AI answering rate only: Starter $0.16/min, Professional $0.14/min, and Business $0.12/min.

Your SIP provider continues to bill you separately for the numbers themselves and for any carrier-side traffic. See Billing for Mylla's per-minute rates.

Editing or removing a linked number

Change the agent assignment

Same flow as any Mylla number — see Numbers → Assigning Numbers to Agents.

Stop using a linked number

Go to Numbers
Click the linked number
Click Release

The number is removed from Mylla but your SIP provider still owns it — calls will stop reaching Mylla the moment you also remove the termination route at your provider.

Move a linked number to Mylla ownership

If you'd rather Mylla own the number instead of you keeping the provider, contact support to start a port-in. See Migration Guide for the full process.

Permissions

Action	Super Admin	Admin	Member
Link SIP trunk	✅	✅	❌
Edit allowed IPs / auth	✅	✅	❌
Release a linked number	✅	✅	❌
View linked numbers	✅	✅	✅