Cloud vs. On-Premise PBX Costs for a 20-Phone Office

Updated October 24, 2026

Two Ways to Equip a Small Office with 20 Phones

A small office can use an in-house PBX connected to a telephone service provider or choose a cloud-based service that hosts the phone system off-site. Both approaches should be evaluated against the same calling requirements, support expectations and ownership period.

The important question is not simply which option has the lowest initial price. It is what your business will pay for equipment, installation, service, licensing and support over the years you expect to use the system.

This comparison uses a hypothetical office with 20 employees and 20 desk phones. The figures are planning examples, not provider quotes, market averages or a guarantee of savings.

What Each Solution Includes

Option 1: An In-House IP-PBX with SIP Trunk Service

The office installs a PBX appliance or runs PBX software on a local server. Its 20 desk phones connect to that system, while SIP trunk service provides the connection for external telephone calls.

The business purchases the necessary equipment and arranges for configuration, security updates, backups and ongoing support. Those responsibilities can be handled by qualified internal staff or a contracted telephone system company.

For this example, the office plans for eight simultaneous external calls. That is an assumed requirement, not a recommendation for every 20-phone business. Actual capacity should reflect busy-period calling, transfers, conferencing and expected growth.

Option 2: A Cloud PBX with 20 User Subscriptions

The provider hosts the PBX, and the office connects its compatible desk phones and applications to the service. This example assumes 20 paid user subscriptions, with one desk phone for each employee.

The provider maintains the hosted platform. The business still needs to plan for its local network, internet access, phone configuration, account administration and employee training.

Ask whether shared phones, common-area phones and additional devices require separate licenses. Twenty physical phones do not necessarily produce the same bill under every provider's licensing model.

Assumptions Used in This Cost Example

• 20 employees, each with one desk phone and one extension.
• 20 new, compatible IP phones at an assumed $125 each.
• Basic calling needs such as an auto attendant, voicemail, transfers, ring groups and after-hours routing.
• An existing office network and internet connection suitable for the selected solution.
• No change in employee count or pricing during the comparison period.
• No financing, equipment resale value or tax benefits included in the calculations.

Both proposals should be checked against the same requirements. Do not assume that texting, recording, video meetings, advanced reporting or application integrations are included in either base configuration.

All amounts below are in US dollars. Substitute written vendor quotes before using this example to make a purchasing decision.

Illustrative Costs for a 20-Phone Office

What the Example Shows

Under these assumptions, cloud service starts with a $3,000 lower upfront cost. The in-house system has a $200 lower monthly budget.

The cloud option costs $600 less during the first year. By the end of three years, the in-house option costs $4,200 less. Over five years, the difference grows to $9,000 in favor of the in-house system.

The initial cost difference is recovered after 15 months: $3,000 divided by $200 in monthly savings. At that point, both examples have a cumulative cost of $11,250.

These results describe this example only. A lower cloud subscription price, higher on-site support costs, an equipment replacement or different licensing terms could change the outcome substantially.

Costs to Add Before Comparing Actual Quotes

The example excludes the following items. Include them wherever they apply, and make sure a cost has not already been included elsewhere in the proposal.

• Taxes, regulatory charges and provider-imposed fees.
• New cabling, PoE switches and network improvements.
• Battery backup equipment and replacement batteries.
• Internet upgrades or a secondary connection.
• Number porting, shipping and activation charges.
• International calling, usage overages and toll-free service.
• Business texting, fax, recording and storage requirements.
• Remote-user setup and security requirements.
• Internal administration time beyond the stated allowances.
• Equipment failures, replacements and future upgrades.
• Price increases at renewal and contract exit costs.

Existing phones may change the calculation. Ask each vendor to confirm compatibility, support status and provisioning requirements before assuming that your current devices can be reused.

Compare Features as Well as Costs

A lower price is useful only if the proposed system meets your operational requirements. Ask both vendors to demonstrate the call flows your office uses every day.

• How incoming calls reach the receptionist or appropriate team.
• How staff transfer, park and retrieve calls.
• What happens when all available call capacity is occupied.
• How voicemail and after-hours calls are handled.
• How employees answer calls while away from their desks.
• How emergency calling and location information are configured.
• What happens during an internet, power or equipment outage.
• Who handles updates, backups and service problems.

If video meetings and messaging are important, compare those requirements separately. An integrated service may be useful, but do not assign value to features employees will not use.

See our guide to integrated voice, video and messaging for additional considerations.

Which Approach Fits Your Small Office?

Consider an In-House PBX When:

• You want to evaluate a larger initial purchase against potentially lower ongoing costs.
• Your staffing and phone requirements are relatively stable.
• You have access to dependable installation and ongoing support.
• You want direct control over the locally installed system.
• Your existing equipment may be suitable for reuse.

Consider Cloud Service When:

• You prefer a smaller initial investment in PBX equipment.
• You want the provider to maintain the hosted PBX platform.
• You want to evaluate a subscription-based approach for office and remote employees.
• The included applications and features match your needs.
• The complete recurring cost is acceptable over your expected ownership period.

Request Comparable Proposals

Give each vendor the same requirements: 20 phones, the required extensions and numbers, busy-period calling demand, essential features and support expectations. Ask for itemized upfront and recurring charges, plus one-, three- and five-year totals.

Compare the result with your existing system's actual costs. Neither cloud service nor an in-house PBX is automatically the least expensive choice for every office.

For more planning guidance, see cloud vs. on-premise PBX, SIP trunk service and our small-business VoIP checklist.

Looking for proposals for your office? Complete our questionnaire to request phone system quotes tailored to your requirements. USA only.

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Frequently Asked Questions About a 20-Phone Office System

Is a cloud PBX cheaper than an in-house PBX for 20 phones?

It depends on equipment costs, subscription rates, licensing and ongoing support. In the illustrative comparison above, cloud service costs less upfront and during the first year, while the in-house system costs less over three and five years. These results reflect the stated assumptions, not guaranteed savings. Compare itemized quotes over the same ownership period.

How much does a phone system for a 20-person office cost?

In this page's hypothetical example, the in-house PBX costs $6,000 upfront plus a $350 monthly budget. The cloud solution costs $3,000 upfront plus a $550 monthly budget for 20 users. Both examples include 20 desk phones. These are planning figures rather than vendor quotes, and the listed exclusions must be added where applicable.

Does an office with 20 phones need 20 outside phone lines?

Do not assume that the number of phones determines the required outside calling capacity. This example uses 20 extensions with an assumed capacity of eight simultaneous external calls for the in-house PBX. Ask the installer to assess busy-period calling, transfers, conferencing and expected growth before selecting service capacity.

Can we reuse our existing desk phones?

Have each vendor verify your exact phone models, support status and provisioning requirements before including reuse in the proposal. Do not assume that phones supported by your current system will work with the replacement. The cost example on this page budgets for 20 new phones, so confirmed reuse would change the calculation.

What should we ask vendors to include in a phone system quote?

Request itemized equipment, installation, licensing, telephone service and support charges. Also ask about taxes and fees, number transfers, network upgrades, optional features, contract terms and renewal pricing. Give each vendor the same 20-phone requirements and request total costs over one, three and five years.

Can a business deduct the full cost of an on-site PBX in the first year?

Possibly. For US federal income tax purposes, qualifying PBX equipment and business phones may be eligible for a first-year deduction under Section 179 or applicable bonus depreciation rules, rather than being depreciated over several years. The equipment must be placed in service during the tax year, and eligibility, business use, deduction limits and other requirements apply.

A full deduction is not the same as reimbursement of the purchase price: it reduces taxable income, not taxes dollar for dollar. Ask your tax professional which equipment, software and installation costs qualify, and whether your state follows the same rules. The cost comparison above does not include potential tax benefits for either option.