What is VoIP?
VoIP, or Voice over Internet Protocol, is the technology that lets you make phone calls over an internet connection instead of a traditional phone line. Your voice is turned into small digital packets, sent across the network and turned back into sound at the other end. If you have ever made a call from WhatsApp, Zoom or a softphone, you have used VoIP.
For businesses it is the base of the modern phone system. It is what lets a company run calls through software, keep a number when staff work from home and connect calls to a CRM. This guide explains how VoIP works, what call quality depends on, how it compares with other options and how to get started. For the wider system built on top of it, see our guide to cloud telephony.
How VoIP works
- Your voice is captured. The microphone produces an analogue signal that is sampled into digital data.
- A codec compresses it. Codecs such as Opus or G.711 balance sound quality and bandwidth.
- Packets are sent. The audio is split into tiny packets, typically every twenty milliseconds, carried over the Real-time Transport Protocol.
- The call is set up by signalling. The Session Initiation Protocol, explained in our SIP trunking guide, starts, answers and ends the call.
- The far end rebuilds the sound. A small buffer puts packets back in order and the codec turns them into audio.
The full background is covered in the article on voice over IP. The important idea is that a call is no longer a dedicated circuit; it is a stream of data that shares the network with everything else.
VoIP vs landline vs mobile calls
| Landline (PSTN) | Mobile network | VoIP | |
|---|---|---|---|
| Carried over | Copper or fibre circuit | Cellular network | Internet connection |
| Needs special hardware | Yes | Phone and SIM | No: apps and IP phones work |
| Adding a line | Wait for installation | New SIM | A few clicks |
| International calls | Often expensive | Often expensive | Usually low per-minute rates |
| Works when away from the office | Only with forwarding | Yes | Yes, with an app or browser |
| Features such as menus and recording | Extra equipment | Limited | Built in |
| Depends on | Line and power | Coverage | Internet quality |
What call quality depends on
Calls sound good or bad because of the network, not the technology. Three measures matter, and each can be tested before you commit.
| Measure | What it is | Good target | What goes wrong |
|---|---|---|---|
| Latency | Time for sound to travel one way | Under about 150 ms | Talking over each other |
| Jitter | Variation in the time between packets | Under about 30 ms | Choppy or robotic audio |
| Packet loss | Packets that never arrive | Under about 1 percent | Words cut out |
Bandwidth is rarely the problem. One call uses very little. The trouble is usually congestion on a shared connection, weak Wi-Fi or a router that does not give voice priority.
- Use wired connections or good 5 GHz Wi-Fi for desk phones and agents.
- Enable voice priority, known as quality of service, on your router if it supports it.
- Use headsets with noise cancellation; they improve audio more than most network changes.
- Test from the actual place calls will be made, at busy times of day.
- Keep a fallback, such as forwarding to a mobile, for outages.
The International Telecommunication Union publishes the standards used to judge voice quality, and our SIP trunking service lets you connect an existing phone system to the same network.
VoIP for business: what you can do with it
| Capability | What it gives you |
|---|---|
| Virtual numbers | Local or toll-free numbers in many cities and countries; see virtual numbers |
| IVR and routing | Menus and rules that send callers to the right team; see IVR |
| Click-to-call | Calls placed from a web page or CRM; see click-to-call |
| Recording and analytics | Quality review, training and reporting on volumes and waits |
| Remote and mobile work | Agents answer from anywhere on a laptop or phone |
| Integrations | Calls logged into your CRM or helpdesk through an API |
Our voice product brings these together, and the API reference shows how to place and receive calls from your own software.
Cost of VoIP
VoIP costs usually have three parts: a monthly charge per user or per number, per-minute charges for calls that leave the VoIP network, and optional extras such as recording storage or advanced features. Calls between VoIP users on the same platform are often free. Set against a traditional line, the saving comes mainly from international and long-distance calls and from not paying for hardware and installation. Prices vary by country and provider, so ask for a quote that includes everything you expect to use. The pricing page and the cost calculator help with estimates.
Security and compliance
A phone system on the internet is a target, and the most common attack is toll fraud: someone gains access to your system and places expensive calls to premium destinations. Defend against it with strong, unique passwords, restricted access by IP address where possible, limits on international destinations, alerts for unusual spending and encryption for signalling and audio. Ask your provider how it monitors for fraud and whether it can set spending caps.
Regulation also applies. Number use, emergency calling, call recording consent and marketing calls are regulated and differ by country. Our compliance overview and country rules guide list the main points.
A minimal call flow in plain language
Incoming call to +91 80 1234 5678
-> Greeting: "Thank you for calling Telnxo. Press 1 for sales, 2 for support."
-> 1: ring the sales group for 20 seconds, then voicemail
-> 2: ring support; if no answer in 30 seconds, offer a callback
-> No key pressed: connect to receptionCommon VoIP problems and how to fix them
| Symptom | Likely cause | Fix |
|---|---|---|
| Choppy or robotic voice | Jitter or a busy Wi-Fi network | Use a wired connection and enable voice priority |
| Echo | Speakerphone feedback or a poor headset | Use a headset and lower the speaker volume |
| One-way audio | Firewall or NAT blocking audio packets | Allow the provider's media ports and use a SIP-aware setup |
| Calls drop after a minute or so | Timeouts in the router or firewall | Adjust keep-alive settings and check the SIP ALG option |
| Delay in conversation | High latency, often from a distant data centre | Choose a provider with a nearby point of presence |
| Cannot register the phone | Wrong credentials or blocked port | Check the account details and the network rules |
Most of these problems are found within a day of a pilot, which is the main reason to start small. When something does go wrong, note the time, the number called and what you heard, because a provider can use that to trace the call. Our SIP trunk set-up guide and the troubleshooting hub cover the settings that most often cause trouble.
It also helps to plan for growth. A system that works for five agents can struggle at fifty if the office connection is shared with video calls, backups and software updates. Measure the connection at the busiest time of day, count the simultaneous calls you expect and leave headroom. If you outgrow one connection, a second one from a different provider also gives you resilience when one goes down.
How to get started with VoIP
- Write down who calls you, what they want and who should answer.
- Test your internet connection for latency, jitter and loss.
- Choose a provider with coverage in your countries and clear pricing.
- Move or request your numbers, planning the port for a quiet time.
- Pilot with one team, then expand.
- Review call quality reports each month and adjust.
VoIP did not change what a phone call is. It changed what a phone call costs and where it can happen.
Talk to our voice team. Tell us your countries and team size and we will plan the set-up with you.
Frequently asked questions
What is VoIP?
VoIP stands for Voice over Internet Protocol. It is a technology that converts voice into digital packets and sends them across an internet connection, so phone calls can be made without traditional phone lines.
How does VoIP work?
Your voice is captured and compressed by a codec, split into small packets, sent over the internet and reassembled in order at the other end, where it is turned back into sound. Call set-up usually uses SIP.
What do I need to use VoIP?
A reliable internet connection, a device such as a phone, laptop or mobile app, and an account with a VoIP provider that gives you a number or extension.
Is VoIP better than a landline?
For most businesses it is cheaper and more flexible, with easy remote work and features such as menus and recording. A landline can be more predictable in areas with poor internet, and does not depend on power in the office in the same way.
Does VoIP work without internet?
No. If the internet connection fails, calls fail unless you have a fallback such as call forwarding to a mobile or a second connection.
How much bandwidth does a VoIP call use?
A call typically uses a small amount, commonly tens of kilobits per second in each direction depending on the codec. What matters more than speed is stability: low delay, low jitter and little packet loss.
Is VoIP secure?
It can be, if you use encryption such as TLS and SRTP, strong passwords, restricted access to your phone system and a provider that monitors for fraud. Unprotected systems can be abused for toll fraud.