VoIP Phone Systems Explained: Users, Lines, and Call Channels

Many businesses assume that if they have 10 employees, they can handle 10 phone calls at the same time.

In reality, that depends on how the phone system is built.

Some VoIP phone systems include one call line per user, while others use SIP channels, which control how many calls can happen at once.

Understanding the difference between users, lines, and channels can help you choose the right phone system and avoid unexpected costs.

Phone System Model Comparison

Model 1: Per User Call Capacity

Users: 👤👤👤👤

Calls: 📞📞📞📞

Model 2: PBX With SIP Channels

Users: 👤👤👤👤👤👤👤👤👤👤

Calls: 📞📞📞📞

Phone Systems With Built-In Call Capacity

Some modern hosted VoIP platforms include one concurrent call per user.

This means every user automatically has the ability to be on a call at the same time.

For example:

Number of Users	Maximum Concurrent Calls
3 users	3 calls
5 users	5 calls
10 users	10 calls

With this model, pricing is usually per user, and the call capacity grows automatically as your team grows. This type of system is often ideal for small businesses because it is simple to understand and there are no extra calculations needed. If you add another employee, you simply add another user, and the system automatically supports another call.

PBX Phone Systems Using SIP Channels

Other phone systems use a PBX platform combined with SIP trunks.

In this setup, pricing is usually based on two things:

Users (extensions)
Call channels

Call channels control how many calls can happen at the same time, regardless of how many users exist. These channels are typically delivered using Session Initiation Protocol (SIP) technology.

For example:

Users	Channels	Maximum Concurrent Calls
10	4	4 Calls
15	6	6 Calls

Even though the company may have 10 employees, only 4 calls can happen at once unless additional channels are purchased.

PBX systems usually require a dedicated server. If your number of channels is near equivalent to the number of users, a per-user system (where channels are included) is often the better option. However, if you have many users but only a few calls happening simultaneously, a PBX with added users and channels can be more cost effective.

Why Some Businesses Choose the Channel Model

The channel model is not necessarily a disadvantage. In many cases, it can actually reduce costs.

For example, a company might have:

20 employees
Only 5 staff regularly on the phone

In this situation, the business may only need 5 call channels, which can be more cost effective than paying for 20 simultaneous call paths.

This model works particularly well for:

1. Offices where most staff do not make calls

2. Larger businesses looking to optimise telecom costs

3. Teams that mainly receive calls rather than make them

How Many Concurrent Calls Does Your Business Actually Need?

Many businesses overestimate how many calls happen at the same time. In reality, most offices only have a small percentage of staff on the phone simultaneously.

A rough guide:

1–5 employees

2-3 Calls

5–10 employees

3-6 Calls

10–20 employees

5-10 Calls

For example, a business with 12 employees may only ever have 5 or 6 calls happening at once. Understanding your peak call activity can help ensure you choose a system that provides enough capacity without paying for unnecessary call channels.

Which Phone System Is Best?

Both models have advantages depending on how your business uses the phone system.

Feature	Per User Systems	PBX With Channels
Pricing model	Per user	User plus channels
Call limits	Usually one call per user	Limited by channel count
Best for	Small teams	Large organisations
Scaling	Add more users	Add more channels