What Is IP Telephony (VoIP) and How It Works for Business
Basics4 minInnovialabs editorial team
In short
IP telephony (VoIP) carries voice over the internet or the office network instead of copper phone lines, so calls can be answered on any device, routed flexibly between staff and connected to your CRM.
IP telephony in plain words
IP telephony (VoIP, Voice over IP) sends voice as data packets over an IP network: the internet or your office LAN. Instead of a dedicated phone cable, the call travels over the same connection as email and websites.
For a business this means:
- a number is not tied to a specific cable or desk;
- an employee can answer on a desk phone, a laptop or a smartphone;
- calls can be recorded, routed by rules and logged in your CRM.
How it works: SIP and codecs
SIP (Session Initiation Protocol) is the main signalling protocol. It handles the "control" side of a call: dialling, locating the other party, ringing, setting up and ending the connection. The voice itself travels separately, usually over RTP.
A codec defines how voice is compressed:
- G.711 — almost no compression, good quality, needs more bandwidth;
- G.729 — heavy compression, saves bandwidth, slightly lower quality;
- Opus — a modern adaptive codec that adjusts to network conditions.
Call quality depends less on raw internet speed and more on latency, jitter (variation in delay) and packet loss. That is why office networks often prioritise voice traffic with QoS.
Virtual numbers
A virtual number is a number from a carrier that is not bound to a physical line. Calls to it reach your PBX over the internet. You can:
- get a local number or a number in another city;
- keep your existing number when switching (if the carrier supports porting — check the terms);
- use separate numbers for ad campaigns to see where calls come from.
IP phones or softphones
| IP phone | Softphone | |
|---|---|---|
| What it is | A dedicated desk device | An app on a computer or smartphone |
| Connection | Network cable, often powered via PoE | Over the device's internet |
| Pros | Familiar, stable, independent of the PC | Cheaper, mobile, works from home |
| Cons | Hardware to buy | Depends on headset, laptop and Wi-Fi |
| Best for | Reception, high-call-volume teams | Field managers, remote staff |
Many teams use both: a desk phone plus a mobile app on the same extension.
Call routing and IVR
Routing decides where an incoming call goes:
- ring all several employees at once;
- sequential ringing one by one;
- a queue with hold music;
- different rules during and after business hours;
- forwarding to a mobile if nobody answers.
IVR (voice menu) is the "Press 1 for sales" part. It helps split calls between departments, but a long menu frustrates callers. Keep it short: two to four options and a way to reach a person right away.
What you need to move off landlines
- Reliable internet with headroom for voice, ideally with a backup link.
- A PBX: cloud-hosted by a provider or your own in the office.
- Numbers: ported existing ones or new virtual ones.
- Devices: IP phones, headsets, apps.
- Network: a PoE switch and QoS settings if needed.
- Call flows: who answers, what happens at night, whether calls are recorded.
- A transition period: keep the old lines until you confirm everything works.
Common mistakes
- Not testing the network for latency and loss — calls sound choppy and drop.
- No plan for what happens when the internet goes down.
- A long voice menu with no way to reach a human.
- Not informing callers about recording where that is required.