How Many Simultaneous Calls Does Your UAE Office PBX Need?

An office may have 20 desk phones but need only a few external calls at the same time. A smaller team may handle several customer calls simultaneously. That is why the number of extensions alone is not enough to size an IP PBX.

For a UAE office phone project, ask: how many calls must the system carry during the busiest part of the working day? The answer affects the PBX model, telecom service, network and call routing. This guide helps you prepare a practical capacity estimate before requesting a quotation.

Extensions, simultaneous calls and SIP channels are different

• Extension: a user or endpoint registered to the PBX, such as a desk phone, reception phone or softphone.
• Simultaneous calls: calls active at the same time. Check how the manufacturer measures capacity for the exact model and features.
• SIP trunk channels: the external calling capacity supplied under your telecom service.

A PBX can support more extensions than concurrent calls. For example, the official Yeastar P-Series comparison lists the P520 with 20 users and a maximum of 10 concurrent calls. This illustrates why user count and call capacity must be checked separately; it is not a recommendation for every 20-person office.

The external service must also have enough capacity for calls entering or leaving the office. Ten telephone numbers do not automatically mean ten simultaneous external calls.

Start with the busiest call period

Review a representative busy period rather than a quiet daily average. Where available, use PBX call reports to identify the peak. Record:

1. The highest number of inbound calls active at once.
2. The highest number of outbound calls active at once.
3. Reception, sales and support requirements, including waiting callers.
4. Remote staff and softphone users who need access.
5. Required conference, forwarding and recording features.

A practical office example

Imagine an office with 18 employees and 15 desk phones. At its busiest point, reception handles two inbound calls, sales makes three outbound calls and a manager takes another external call. That is six external calls at once, before accounting for waiting callers or other call legs.

The installer should confirm the real peak and allow for realistic growth. The requirement is not automatically 15 external channels simply because there are 15 phones. Compare both the PBX capacity and the provider-confirmed channel capacity with the agreed call flow.

Document how calls move through the business

Call routing does not create extra external capacity. It determines how callers reach the right person and how the system handles busy periods. Write down the following before installation:

• Main company number and any direct numbers.
• Reception and department ring groups.
• IVR or auto-attendant menu.
• Queues, available agents and expected waiting callers.
• Office-hours, after-hours and voicemail destinations.
• External forwarding and approved remote users.
• Outbound caller ID and calling permissions.

If a call is forwarded to an external mobile, ask the installer how the additional call leg affects the proposed system and telecom service. Check the actual configuration instead of assuming that forwarding is capacity-free. Our guide to office IP phone ring groups and call routing explains the planning considerations.

Confirm the telecom connection before cutover

A PBX may support more calls than the external connection can carry. Obtain confirmation from your telecom provider of the available service, channel count, activation responsibilities and any number-transfer requirements.

Record whether the office uses a SIP trunk, analogue lines or another supported interface. An installer can configure the office phone system, but provider account changes, service activation and credentials must follow the provider’s process. Never send passwords or telecom credentials in an ordinary enquiry message.

Check the network behind the IP phones

A successful installation also depends on the office network. Review the desk locations and structured network cabling, available switch ports, phone power requirements and router/firewall configuration.

• Confirm whether each handset supports Power over Ethernet (PoE).
• Check the switch’s compatible PoE standard and total power budget.
• Assess voice VLAN and quality-of-service requirements.
• Check the connectivity required by the selected phone service.
• Plan backup power for the PBX, switch and router where required.

Grandstream’s VLAN guidance explains how voice/data separation can support network segmentation and voice-priority configuration. The design must match the installed equipment. A generic configuration should not be applied without checking the site.

Before reusing an existing switch, review our PoE switch planning guide for IP phones. Send the switch and firewall model numbers and clear cabinet photos so compatibility can be assessed.

Compare proposals using the same requirements

Ask every proposal to identify the exact PBX model, current and future users, concurrent-call capacity, provider channels, required interfaces and any recurring licences. It should also describe installation, testing and handover.

For a Grandstream-based project, see our Grandstream PBX installation and configuration guide. ZD Computer Trading can assess the equipment and network requirements as part of an office phone project. A wider office IT infrastructure assessment can help identify cabling or network work needed alongside the phones.

Agree on acceptance checks and handover

Before the work is signed off, test the agreed number of concurrent calls, inbound and outbound routes, transfers, ring groups and after-hours rules. Check call quality at representative desks. The handover should include the extension list, call-flow record, configuration backup and administrator ownership arrangements.

What to send for a UAE business quotation

• Company name, Trade License and TRN copies.
• Office address and Google Maps location.
• Contact person’s name and mobile number.
• Required extensions, desk locations and expected peak call activity.
• Existing PBX, phone, router/firewall and switch models.
• Clear photos of the existing phone system and network cabinet.
• Provider name and current line type, without passwords.

If troubleshooting is needed, include the fault description and a safe one-minute video of the relevant setup. Avoid filming passwords, customer records or private conversations. Home users do not need a Trade License; provide the name, contact details, address, device model and issue instead.

Frequently asked questions

How many simultaneous calls does a 20-person office need?

There is no universal number. Measure the busiest inbound and outbound activity, consider queues and forwarding, then allow for realistic growth. Check this against both PBX capacity and provider channels.

Do internal calls count towards PBX capacity?

Capacity definitions depend on the manufacturer, model and features. Confirm how the proposed system counts internal calls, external calls and additional call legs rather than assuming all vendors use the same method.

Can we reuse our existing PBX?

Possibly. Share its exact model, installed modules, firmware information, current extensions and required changes. Available capacity and compatibility must be checked before promising reuse.

Does every IP phone need a PoE switch?

No. The power method must match the handset. Supported phones can use a compatible PoE switch; others may need the correct power adapter. Check the phone and switch specifications.

Request an IP phone and PBX assessment in the UAE

Planning call capacity helps prevent an unsuitable equipment purchase or an unexpected limit after installation. ZD Computer Trading can review your requirements and prepare a written scope for IP phones, PBX configuration and related network work.

WhatsApp: +971 50 886 3312
Office: +971 4 393 1778

Send the requirements above to request a quotation. Final equipment, provider services, licences, installation, pricing, availability, warranty and support scope will be confirmed in the written quotation.