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Documentation › Phone system

Connect your carrier (SIP trunk)

Keep the phone numbers your customers already know: connect your carrier’s SIP trunk, send each number where it belongs, and let staff call out through it.

Last updated 19 September 2026

Download this guide (PDF) Try it free

At a glance

  • A SIP trunk is your line to the outside world, rented from a carrier over the internet instead of copper.
  • You keep your carrier and your numbers. Filantis connects to the trunk you already pay for.
  • Each number can ring somewhere different — the main line to a call menu, the sales number to the Sales team.
  • Staff call out through a dial route, such as “dial 9, then the number”.
  • The Trunks page shows the line's health — registered, rejected or offline — and re-checks it on demand.

On this page:

  1. How calls come in and go out
  2. What to ask your carrier
  3. Add the trunk
  4. Route each number
  5. Check it is connected
  6. Let staff call out
  7. Fax, caller ID and other lines
  8. Questions

1How calls come in and go out

Incoming calls travel from the public network through the carrier's SIP trunk to Filantis, which routes each number; outgoing calls go the other way through a dial route Your customers any phone, anywhere Your carrier the SIP trunk +91 141 400 0000 IN OUT Filantis routes each number and each dial-out Call menu 6001 main number Sales team sales number 1001 Reception direct line
One trunk, many numbers. Each number is routed on its own; outgoing calls leave the same way.

2What to ask your carrier

Your carrier's welcome email usually has everything. If not, ask for these — the last column is where each goes in Filantis:

Ask forLooks likeFilantis field
HostThe carrier's SIP server, e.g. sip.carrier.exampleHost
Port and transportUsually 5060 over UDP; 5061 for TLSPort, Transport
Username and passwordFor carriers that register your lineUser, Password
Authentication usernameOnly if it differs from the usernameAuth Username
Outbound proxyOnly if the carrier gives you oneOutbound Proxy
Your numbers (DIDs)Every number on the line, in +country formatMain Phone Number, DID Numbers
CodecsG.711 (PCMU/PCMA) is the safe choice; G.722 for HD voiceCodec Preference
Key presses (DTMF)Almost always RFC 2833DTMF Mode
ChannelsHow many calls the line carries at onceMax Channels
Register

Username and password

Filantis signs in to the carrier and keeps the line open. Works from any internet connection. Tick Register with provider.

By IP

Your server's address

The carrier sends calls to your Filantis server's public address and trusts it. Give them that address; leave Register with provider unticked.

3Add the trunk

  1. Open Phone & Extensions → Trunks and click Add Provider.
  2. On Phone Configuration, give it a Phone Name — “Airtel main line” — and set Phone Type to SIP Trunk (Internet / Cloud Provider).
  3. Fill in Host, Port, Transport and, for a registering line, User and Password.
  4. Enter the Main Phone Number in +country format and choose its Inward Destination — where calls go when no other rule matches.
  5. Click Connect Phone.

Your plan sets how many trunks you can connect: 1 on Mini and Small, 3 on Medium, 10 on Large.

4Route each number

If your carrier gave you more than one number, open the DID Numbers tab and click Add DID Number for each. Give the number in +country format, then choose where it goes. A trunk holds up to 150 numbers.

NumberDestinationWhy
+91 141 400 0000Call Attendant 6001The number on your website: greet and sort callers
+91 141 400 0011Department — SalesPrinted on the sales brochure
+91 141 400 0022User Extension — 1001The manager's direct line
+91 141 400 0099Department Voicemail — AccountsA number only for leaving messages

Any number on the trunk that is not listed goes to the Inward Destination. DID numbers are saved with the trunk: after adding them, go back to Phone Configuration and click Connect Phone.

Every call that arrives on the trunk ends at one of your destinations — its number's own, or the Inward Destination. It is never passed back out through the trunk, so nobody can use your line to make calls on your account.

5Check it is connected

The Trunks list shows each line's Registration:

  • Registered — the carrier accepted the sign-in
  • Rejected — wrong username or password
  • Unregistered — not signed in yet
  • Unknown · Not applicable — IP-authenticated lines never register

Click Register on a line to sign in again now and see the carrier's answer on the spot. Then ring your main number from a mobile: it should reach the destination you chose.

6Let staff call out

Outgoing calls need a dial route: a rule that says which dialled numbers leave through which trunk. Most offices want “dial 9 for an outside line”.

  1. Open Call Control → Dial Routes and click Add Dial Rule.
  2. Rule Name: “Outside line”. Priority: 10 — lower numbers are tried first.
  3. Pattern 9, matched as Prefix Match.
  4. Trim First N Digits: 1 — so the 9 is removed before the call leaves.
  5. Destination: Trunk (dial the number out) → your carrier. Add a Failover Destination if you have a second trunk.
1Priya dials9 98290 12345
2“Outside line” matchesstarts with 9
3Trims one digit98290 12345
4Leaves through the trunkand rings the mobile
A dial route in action. Internal extensions are never affected: they always win over a route.

Patterns can be Exact Match (one number), Prefix Match, a Number Range or a Regular Expression. Append Number adds digits after trimming — an international access code, for example. A dialled number that matches no route is not called.

Emergency numbers have their own page — Call Control → Emergency — so 112, 911 or 999 always leave through a working trunk and can alert your team. Set it up before you rely on Filantis for outside calls.

7Fax, caller ID and other lines

  • Faxes — tick Receive faxes on this phone and Filantis tells a fax from a voice call, sending faxes to a fax machine, an email address as a PDF, or a printer. Calls on that trunk are answered a moment before they ring. Set the fax devices up on Printers & Fax.
  • Caller ID — CID Masking - Inbound and - Outbound on the trunk choose what name and number are shown; the CRM tab looks callers up in your contacts.
  • Other kinds of line — Phone Type also covers PRI (T1/E1) and analogue lines through a gateway, and a WebRTC trunk for browser softphones.

8Questions

Do I have to change carrier?

No. Any carrier that offers a standard SIP trunk works, and your numbers stay with them. If you have no trunk yet, most carriers set one up in a day.

Can I have two carriers?

Yes, on plans with more than one trunk. Route numbers on each, and use the Failover Destination of a dial route to switch to the second carrier when the first is down.

A number rings the wrong place.

Calls for a number that is not on the DID Numbers tab go to the Inward Destination. Check the number is listed exactly as the carrier sends it, in +country format, and that you clicked Connect Phone after adding it.

How many calls can I make at once?

Whichever is lower: the channels your carrier sells you, or your plan's simultaneous calls — 4 on Mini, 8 on Small, 16 on Medium, 24 on Large. Calls between extensions do not use the trunk.

Is the connection encrypted?

Choose TLS as the Transport if your carrier supports it, and signalling travels encrypted. In the United States, Settings → STIR/SHAKEN signs your outgoing caller ID.

Keep your numbers. Lose the phone box.

Filantis replaces the PBX cupboard with software that runs in our cloud or on a small server in your office — and bills, staff and bookings live in the same place as the calls.

  • Any carrierStandard SIP trunks, PRI and analogue lines.
  • Every number routedMenus, teams, people and mailboxes.
  • Safe by designIncoming calls are never dialled back out.
Create my free workspace See the phone system

What to do next

Give callers something to hear with Build a call menu (IVR), and put phones on desks with Set up desk phones.

Still stuck?

Write to hello@filantis.com with your workspace name and what you were trying to do.