Connect a phone number to your agent
Bring a Twilio number or any SIP provider, point it at an agent, and start taking real calls. Inbound and outbound trunks explained.
7 min readUpdated 26 August 2026
Everything up to this point works in the browser. A phone number is what puts your agent on the actual telephone network.
Open Phone Numbers in the sidebar. The page is titled SIP Trunks and describes itself as connecting, routing and managing your inbound and outbound numbers.
Inbound and outbound are different things
The Connect number button offers Inbound Trunk or Outbound Trunk, and the choice is not cosmetic.
Note
An account can have both, and usually does. They are configured separately because they solve separate problems.
| Trunk | What it does | You need it when |
|---|---|---|
| Inbound | Receives calls made to your number and routes them to an agent | People will ring you |
| Outbound | Lets an agent place calls from your number | You will ring people, including campaigns |
Two ways to bring a number
Choosing Inbound Trunk opens Add New Inbound Phone Number and asks you to choose an integration type.
- Import from Twilio, described as bringing an existing Twilio number.
- Custom SIP Integration, described as connecting any SIP provider directly.
Both end in the same place: a trunk in your list, pointed at an agent. Twilio is the shorter path if that is where your number already lives. Custom SIP is what you use for everything else.
Filling in the form
The form has three parts.
| Section | Fields |
|---|---|
| SIP Configuration | Name, Phone Number with a country code selector, and optional SIP Username and SIP Password |
| Allowed Sources (Optional) | Allowed Numbers and Allowed Addresses |
| Agent Configuration | Select Agent Configuration |
Name is for you. Name it after what the line is for, because a list of numbers is unreadable and a list of purposes is not.
Agent Configuration is the part that matters most and is easiest to forget. A trunk with no agent selected is a number that rings into nothing.
The outbound form is shorter
Choosing Outbound Trunk opens Add New Outbound Phone Number, with the same two integration choices. The form that follows is smaller, and the differences tell you what each trunk is for.
| Field | Inbound | Outbound |
|---|---|---|
| Name | Yes | Yes |
| Phone Number | Yes | Yes |
| SIP Address | No | Yes, in the form sip.provider.com |
| SIP Username and Password | Optional | Optional |
| Allowed Sources | Yes | No |
| Agent Configuration | Yes | No |
Outbound asks for a SIP address because it has to know where to send calls. It does not ask for an agent, because on an outbound call the agent is chosen when the call is placed rather than being fixed to the number. And it has no Allowed Sources, because nothing is arriving.
What Allowed Sources is for
This section is optional and worth understanding before you skip it. Allowed Numbers takes a list of phone numbers, in the form the placeholder shows. Allowed Addresses takes IP ranges in CIDR form, such as 1.2.3.4/32 or 10.0.0.0/24.
Setting either one restricts what can reach this trunk. Left empty, anything that can route to the number gets through.
Tip
For a public support line, leave these empty. For a trunk that should only ever be reached by your own switch, an address restriction is a cheap way to make that true rather than assumed.
Reading the list afterwards
Each row shows the trunk name, whether it is Inbound or Outbound, the numbers on it, the agent or dispatch it points to, whether Krisp noise cancellation is on, and the SIP trunk ID.
The counts at the top summarise the same thing: how many trunks, how many inbound, how many outbound, and how many numbers in total.
After it is connected
Ring the number. That sounds obvious and it is the step people skip, because it feels like configuration should be enough.
A call over the phone network is not the same as a browser test. Phone audio is narrower, callers are in noisier places, and the telephony leg adds its own delay. An agent that sounded good in the dashboard is worth hearing on a real call before you point traffic at it.
Common questions
- My number rings but nothing answers. What is wrong?
- Check that an agent is selected on the trunk. A trunk with no agent has nowhere to send the call. It is the most common cause by a distance.
- Do I have to buy a number from NexaVoxa?
- No. You bring your own, either from Twilio or from any SIP provider you already use.
- Do I need an outbound trunk if my agent only answers calls?
- No. Inbound is enough. Add outbound when you want the agent to place calls, including for campaigns.
- What is the SIP trunk ID for?
- It identifies the trunk when you are debugging with your telephony provider or asking support about a specific line.
- What does Krisp do?
- It is noise cancellation on the line, shown per trunk in the list so you can see at a glance where it is on.
- Can two numbers point at the same agent?
- Yes. Several trunks can select the same agent, which is how one agent covers several lines.
Was this helpful?