What is VoIP?

VoIP (Voice over IP) is the technology that carries phone calls over the internet instead of traditional phone lines. It's the foundation of modern business phone systems and AI voice agents.

Written By Catherine Weir

Last updated About 1 hour ago

VoIP stands for Voice over Internet Protocol. It's the technology that carries phone calls over the internet instead of over traditional phone lines. VoIP is the foundation of virtually every modern business phone system, every cloud PBX, every mobile calling app, and every AI voice agent you've ever heard.

When you make a call on Zoom Phone, RingCentral, Microsoft Teams, FaceTime, WhatsApp, or any other modern calling service, you're using VoIP. The audio is digitized, chopped into packets, and sent across the internet just like any other data — then reassembled into sound at the other end.

How VoIP works

  • Audio capture — your voice is converted to a digital signal by your phone or microphone

  • Compression — the signal is compressed using a codec (like G.711, G.729, or Opus) to fit efficiently across the network

  • Packetization — the compressed audio is split into small packets

  • Transmission — the packets travel across the internet using protocols like SIP (for call setup) and RTP (for the audio itself)

  • Reassembly — at the other end, packets are decompressed and played back as sound

All of this happens in real time, usually adding only a few tens of milliseconds of latency compared to a landline call.

Why VoIP matters for modern businesses

  • Cost — VoIP is usually far cheaper than traditional phone service, especially for long-distance and international calls

  • Flexibility — your "phones" can be desk phones, computers, mobile apps, or integrated into business software

  • Features — modern call recording, transcription, CRM integration, and AI-powered analytics are all possible because the audio is already digital

  • Scalability — adding a new line is a software change, not a physical one

  • Remote work — any employee with an internet connection can be "in the office" on the phone system

VoIP requirements and pitfalls

  • Internet quality matters — voice traffic is real-time and sensitive to latency, jitter, and packet loss. Poor network conditions produce audible call quality problems.

  • Power dependency — VoIP phones don't work during power or internet outages unless you have backup. Traditional landlines kept working because they drew power from the phone line itself.

  • E911 considerations — VoIP phones must have correct location data registered for emergency services to reach the right dispatch center. This is different from landlines and requires explicit configuration. See What is E911?.

VoIP and AI voice agents

AI voice agents are natively VoIP products. The AI runs in the cloud, and phone calls arrive as VoIP streams. This is what makes AI voice agents easy to deploy — you don't have to install hardware, run wires, or change carriers. You just forward (or SIP-route) calls to the AI, and it answers.

Related concepts

  • SIP trunking — the specific protocol VoIP call setup uses

  • PBX — the phone system VoIP connects to

  • Softphone — a software VoIP phone

  • E911 — the emergency calling concern specific to VoIP

See it in action

The Receptionist Agent at 365agents is a VoIP-native AI phone agent. Deploy it by forwarding your existing business number — no hardware, no carrier switch, no rewiring.