Phone Systems for Medium Business: How to Size a 20–50 Seat Multi-Site System

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How many phone users does a medium business phone system support?

A medium business phone system should support 20–50 users while allowing different device types, locations, extensions, call queues and business-hour rules. The number of licensed users is only one part of the design; peak simultaneous calls and the way calls are distributed matter just as much.

A 35-person business might need 35 user profiles but only a fraction of those users will be on external calls at the same time. Conversely, a 20-person service team may need more concurrent call capacity than a 50-person professional office if most calls arrive through shared queues.

Start with a user and location register that records:

A practical design should also allow new users to be added without changing the core call flows. Cloud platforms commonly support phones, computers and mobile devices over an internet connection, while hosted PBX systems centralise extensions and routing across locations. (comstel.com.au)

If you need to choose specific handsets, headsets or mobile apps, cover that in a separate business handset and softphone guide.

How many concurrent calls does a 20–50 seat business phone system need?

Concurrent call capacity should be based on the busiest periods, not simply on the number of employees. Review call records, queue activity and peak periods to estimate how many external calls are active, waiting or being transferred at the same time.

Use this basic sizing method:

For example, a 30-seat office may have 10 people who regularly make external calls, three reception or service queues and several staff who occasionally call customers. Its design may need materially more call capacity than a 30-seat office where most communication happens through email or Microsoft Teams.

Do not confuse:

For a more accurate design, use the provider’s call-detail records and queue reports rather than an employee-count rule of thumb. Microsoft’s call-flow guidance also recommends analysing the types and frequency of existing calls before creating auto attendants and queues.

Should a 20–50 seat business choose a cloud or on-premises phone system?

For most 20–50 seat organisations, a cloud phone system is the first option to assess because it can centralise users, numbers and call flows across sites without requiring a PBX server at every office. An on-premises system may still be appropriate where local control, legacy equipment or specialised integration requirements outweigh the operational simplicity of hosted services.

The choice is not simply “cloud is modern” versus “on-premises is reliable”. The better question is whether your locations, internet services, IT capability and call-routing requirements support the operating model you select.

A hybrid approach can be useful during migration. For example, a business may move its main numbers and queues to a hosted platform while temporarily retaining an analogue alarm line, lift phone or specialist device through an appropriate gateway.

How should a multi-site phone system route calls between locations?

A multi-site phone system should give the business one controlled dial plan while still allowing each location to operate its own hours, teams and public numbers. Staff should be able to call colleagues by extension, transfer calls between sites and route customers to the right location without relying on manual forwarding.

Define the following before selecting or configuring the platform:

A simple numbering plan might reserve:

The exact numbering scheme is less important than consistency. Avoid using a different logic at every location, because staff and administrators then have to remember exceptions when transferring calls or troubleshooting extensions.

For multi-site administration, look for one management view with permissions that can be delegated to the right people. Microsoft’s guidance on authorised users describes delegated control for auto attendants and call queues, including separate permissions for users who need to change greetings, hours or queue settings.

Do all locations need their own phone numbers?

No. A business can use one main number, location-specific numbers, direct numbers for selected staff, shared queue numbers or a combination of these. The correct arrangement depends on how customers identify each location and how calls need to be answered.

Use one main number when:

Use separate local numbers when:

Use shared queue numbers when:

When changing providers, Australian businesses can generally retain eligible local numbers through number porting. The ACMA’s Local Number Portability Code sets operational processes and target timeframes, although complex ports and multiple services can take longer than a simple single-number port.

Porting should be treated as a project dependency rather than a last-minute administration task. Confirm the account holder, service address, numbers, billing records, existing services and cutover plan before the new system is configured.

What internet and network capacity does a 20–50 seat VoIP system require?

A 20–50 seat VoIP system needs a business-grade network that can prioritise voice traffic, maintain stable connectivity and separate phone traffic from uncontrolled data usage. The required internet speed cannot be determined from seat count alone because codec choice, video use, concurrent calls, cloud applications and network design all affect performance.

Assess each site for:

Voice quality depends on the complete connection between the phone, local network, internet service provider and hosted platform. NBN’s Traffic Class 1 guidance explains that business-grade voice traffic can use a wholesale traffic class designed for voice, while also noting that the customer experience depends on equipment, software, service design and other factors outside the nbn access network.

Do not assume that buying more bandwidth fixes every voice problem. Congestion, poor Wi-Fi, misconfigured firewalls, packet loss, jitter, inadequate switching or a failing router can affect calls even when a speed test reports a high download rate.

For multi-site businesses, test each office separately. The head office may have an excellent connection while a small branch, warehouse or medical room has unstable internet, weak Wi-Fi or no practical backup path.

How should a business phone system handle outages and after-hours calls?

An outage plan should decide where calls go when a user, location, internet connection or provider service is unavailable. The plan should be designed before installation and tested after configuration.

Cloud routing can help a business continue receiving calls when a local office is unavailable, but it does not remove the need for working internet, power, configured destinations and people available to answer.

At minimum, test:

Avoid promising “zero downtime” or assuming failover works because it appears in a product brochure. A failover route is only useful when its destination, permissions, devices and activation process have been tested.

Which phone system features matter most for 20–50 seats?

The most important features are the ones that make calls easy to answer, transfer, monitor and recover across users and locations. Choose features based on call patterns rather than selecting the longest available feature list.

Prioritise:

Auto attendants should remain simple. Microsoft recommends keeping menu choices to five or fewer and using terminology callers understand; its call-flow design documentation also covers business hours, holidays, queues, overflow and routing destinations.

Avoid adding features that no one will own. Call recording, transcription, CRM integration, SMS, analytics and AI functions can be useful, but each needs a policy, administrator, user workflow and cost assessment.

If you need a detailed feature-by-feature comparison, link this article to a cloud phone system features checklist.

How much should a 20–50 seat business phone system cost?

The total cost depends on user licences, call charges, numbers, handsets, network changes, installation, integrations, support and contract terms. A per-user price alone is not enough to compare proposals.

Request quotes using the same scope:

Do not compare a basic user licence from one provider with a fully managed multi-site proposal from another. Ask each provider to separate recurring charges, one-off charges, optional features and excluded work.

For help scoping the project, use Nexgen Australia’s business communications assessment or request a multi-site phone system consultation.

What should be included in a phone system implementation plan?

A suitable implementation plan should move from discovery to testing, training and controlled cutover. For a 20–50 seat business, the plan should include every site, queue, number, user type and exception route—not just the phones on desks.

A practical plan includes:

The pilot should include the busiest queue and the least reliable location. Testing only at head office can hide the exact problems that affect branches, warehouses and remote users.

For a staged migration, see business phone system installation and porting.

How do you compare phone systems for a 20–50 seat multi-site business?

Compare systems against the business’s call flows, locations, network conditions and administration model rather than choosing solely by brand or monthly licence price. The strongest option is the one that can be operated reliably by the people responsible for day-to-day changes.

Score each proposal against:

Ask the provider to demonstrate your own call flows using realistic examples:

A demonstration using your call scenarios reveals more than a generic product tour. It also exposes whether a feature is included, requires extra licensing or depends on ongoing provider assistance.

Frequently asked questions about phone systems for medium business

Is 20 users too small for a multi-site cloud phone system?

No. A 20-user organisation may benefit from a multi-site design when it has multiple branches, shared queues, remote staff or different operating hours. The system should still be sized around actual call demand and administration requirements rather than user count alone.

Does every employee need a desk phone?

No. Desk phones suit reception, customer-facing teams and fixed workstations, while softphones and mobile applications may suit remote, travelling or infrequent callers. Use a device mix that reflects each role instead of issuing identical hardware to every user.

Can a business keep its existing phone numbers when changing systems?

In many cases, eligible Australian geographic, local-rate and freephone numbers can be ported to a new provider. Confirm number ownership, service details and porting requirements early because complex services or multiple numbers may need additional preparation.

What is the biggest sizing mistake for a 20–50 seat phone system?

The biggest mistake is sizing licences and handsets without measuring concurrent calls, queues, site connectivity and failover requirements. A system can have enough user accounts but still deliver a poor experience if callers cannot reach an available team or a branch loses connectivity.