SIP trunking is an internet-based voice connection that replaces traditional phone lines, enabling AI voice agents to answer your business calls.
Definition
SIP trunking is a method of carrying phone calls over the internet instead of through traditional copper phone lines or PRI circuits. SIP stands for Session Initiation Protocol, and a trunk is a line that carries multiple simultaneous calls. When someone dials your business number, the call travels over the internet to your phone system, answering service, or AI voice agent rather than through the phone company's physical wiring. For service businesses, SIP trunking is the technical layer that makes it possible to have an AI agent answer calls using your existing business phone number without changing anything the customer sees. A standard business internet connection can handle 50 or more simultaneous calls, which eliminates busy signals during peak periods like storm events or power outages. Setup typically takes just a few hours, phone costs drop 40-60% compared to traditional lines, and your existing number ports over without interruption.
Why It Matters for Your Business
SIP trunking is the plumbing that connects AI voice agents to the phone network. Without it, your AI can't answer calls on your business number. Beyond AI, SIP trunking also cuts phone bills by 40-60% compared to traditional lines, handles unlimited simultaneous calls (no more busy signals), and lets you keep your existing phone number. For a service business that runs on inbound calls, busy signals mean lost jobs. SIP trunking eliminates that problem entirely.
How SIP Trunking Works Across Industries
Hood cleaning companies get seasonal call surges before health department inspections. Traditional phone lines can only handle one or two calls at once. SIP trunking lets AI answer 10 or 20 simultaneous calls during a surge without busy signals. Restaurant managers calling to schedule pre-inspection cleaning always get through instead of hearing a busy tone and calling the next company.
When the power goes out, every generator customer calls at the same time. A traditional 2-line phone system means 2 calls get answered and 48 get busy signals. SIP trunking over internet (with battery backup) handles the entire surge. Generator companies that survive on emergency response can't afford to miss calls during the exact moments they matter most.
Compressed air service companies often cover large territories with calls routing between multiple offices or mobile techs. SIP trunking lets one business number route to different locations based on caller area code, time of day, or tech availability. A customer in Phoenix and a customer in Tucson both call the same number but reach the local team.
See how Ironback puts this into practice → Missed Call Text-Back
Before & After AI
Real-World Examples
A standby generator service company had 4 phone lines. During a regional power outage, they received 73 calls in 2 hours. Most got busy signals. After switching to SIP trunking with AI, the next outage saw all 89 calls answered, triaged by severity, and work orders created. They booked 34 service calls in one evening.
A hood cleaning company was worried that switching to AI meant getting a new phone number. SIP trunking ported their existing number that restaurants had been calling for 12 years. Customers noticed no change except that someone always answered now, even at 6am when restaurant managers call before opening.
A compressed air service company with offices in three states used SIP trunking to route calls based on the caller's area code. A factory in Ohio called the same number but reached the Cleveland office. A plant in Texas reached the Houston team. One number, three locations, zero manual call transfers.
Key Metrics
Frequently Asked Questions About SIP Trunking
No. Number porting transfers your existing number to the SIP trunk provider. Your customers keep calling the same number they always have. The only change is on the backend. Porting typically takes 1-5 business days depending on your current provider.
Good SIP trunk providers offer failover options. Calls can route to a cell phone, a secondary location, or a cloud-based AI agent that doesn't depend on your office internet. Generator service companies should especially have failover configured since power outages often affect internet too.
The SIP trunk provider routes your inbound calls to the AI voice platform (like ElevenLabs or Telnyx). When a call comes in on your business number, it hits the SIP trunk, gets forwarded to the AI agent, and the AI answers as your receptionist. The caller has no idea they're not talking to a person in your office.
With a decent internet connection, SIP call quality matches or exceeds traditional phone lines. You need about 100 kbps of bandwidth per simultaneous call. A standard business internet connection can handle 50+ simultaneous calls without quality issues. Jitter and latency matter more than raw bandwidth.
Related Terms
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