What Is SIP Trunking?

SIP trunking is a method of connecting your business phone system (PBX) to the public telephone network over the internet, replacing traditional phone lines (ISDN/PSTN). SIP stands for Session Initiation Protocol — the standard for voice over IP communication.

Think of a SIP trunk as a virtual phone line. Instead of copper wires from the phone company, you get a digital connection that carries voice calls over your existing internet connection.

How Does SIP Trunking Work?

The setup is straightforward:

  1. Your PBX (3CX, FreePBX, Asterisk, Teams, etc.) connects to your SIP trunk provider via the internet
  2. When someone calls your DID number, the call is routed to your SIP trunk
  3. Your PBX receives the call and rings the appropriate extension or phone
  4. For outbound calls, your PBX sends the call through the SIP trunk to the public network

All you need is an internet connection and a SIP-compatible phone system.

Benefits of SIP Trunking

  • Cost savings — typically 40-60% cheaper than traditional phone lines
  • Flexibility — add or remove channels and numbers instantly
  • No hardware — no physical lines to install or maintain
  • Global reach — get local numbers in any country without local infrastructure
  • Unified communications — combine voice, video, and messaging on one platform
  • Business continuity — route calls to backup locations if your office goes down

SIP Trunking vs Traditional Phone Lines

Traditional ISDN lines require physical installation, long-term contracts, and per-channel pricing. Each line supports one concurrent call and costs EUR 20-50/month.

SIP trunks are virtual — they activate instantly, have no contracts, and scale with your business. With DIDfarm, you pay per number (from EUR 1.49/month) with no channel limits.

Which PBX Systems Support SIP Trunking?

DIDfarm SIP trunks work with any SIP-compatible phone system, including:

  • 3CX — popular cloud PBX for small and medium businesses
  • FreePBX — open-source PBX based on Asterisk
  • Asterisk — the most widely deployed open-source PBX
  • Microsoft Teams — Direct Routing for enterprise telephony
  • Cisco CUCM, Avaya IP Office, Mitel MiVoice, and more

Browse our full integration marketplace for setup guides specific to your platform.

How to Set Up a SIP Trunk

Setting up a SIP trunk with DIDfarm takes under 5 minutes:

  1. Create a SIP trunk in your DIDfarm portal
  2. Copy the credentials — server address (sip.didfarm.com), username, and password
  3. Configure your PBX — add the trunk with the credentials
  4. Assign your DID numbers to the trunk
  5. Make a test call — done!