When you call a company and hear «If you know your party’s extension, dial it at any time», the obvious question is: can I just call that extension directly and skip the menu? Yes — in most cases you can, as long as you know the right format. This guide explains, with concrete 2026 examples, what a PBX extension is, how to dial it from outside, how to store it on your phone, and what to do when it does not work.

This article assumes a modern VoIP / cloud PBX environment (the standard in the UK since the ISDN switch-off in 2025), but the same logic applies to on-premises PBX systems with a DISA (Direct Inward System Access) feature enabled.

What is a PBX extension?

A PBX extension is a short internal number (usually 3 to 5 digits) that routes a call to a specific person, team, or queue inside a company. Even though the company publishes a single public phone number, dozens or hundreds of extensions can live behind it. Each one is a logical endpoint, not a physical line.

For a broader view of the technology behind this, see our guide on the best virtual PBX options for businesses. With modern cloud PBX platforms, extensions are not tied to a desk phone. They follow the user across devices: a softphone on a laptop, a mobile app, a browser tab, or a hardware IP phone. In other words, a PBX extension today is a virtual workstation, not a cable in a wall socket. For a broader view of the topic, read our guide on telephone extensions in general.

How do I call a PBX extension directly from my mobile?

There are three reliable ways to reach a specific extension without going through the auto-attendant. Use the one your provider supports.

Method 1: dial the public number, then queue the extension

This is the simplest method and works on any phone. The format is:

<public number>,,<extension>

where each comma is a 1-second pause. Example: to reach extension 203 at the company whose public number is 0800 123 4567, dial:

08001234567,,203

On iPhone, the comma is the standard pause key. On Android, the semicolon (;) is also accepted and means «wait for the system to answer, then send the rest». Both methods work in the UK and most EU countries.

Method 2: use a DDI (Direct Dial-In) number

Many companies, especially in the UK after the ISDN switch-off, give each extension a Direct Dial-In number — a real public number that rings directly on that extension. If your contact shares a DDI, you just save that number in your phone and call it like any other line.

DDIs are convenient but have a small downside: they reveal the structure of the company’s phone system. Most UK providers (BT, Gamma, Vodafone, Vonage, 8×8, Fonvirtual) offer DDI ranges as part of their standard SIP trunk packages.

Method 3: ask the company to enable DISA

DISA (Direct Inward System Access) is a feature in many on-premises PBX systems that lets an external caller reach an internal extension by dialling a short code after the system answers. If the company has it enabled, you will hear a second dial tone after the public number answers, and you can punch in the extension directly.

DISA is increasingly rare in cloud PBX deployments because it is a security risk if not configured carefully (callers could exploit it to make outbound calls at the company’s expense). Modern platforms prefer DDIs over DISA.

How do I save a PBX extension to my phone contacts?

On both iPhone and Android, the trick is to save the number with the pauses and extension already inside, so the phone does the work for you next time you tap «Call».

1. Open your phone’s Contacts app and create a new contact.
2. In the phone number field, type the public number first.
3. Add one or more pause characters. On iPhone, tap the + * # key, then choose Pause (adds a comma) or Wait (adds a semicolon).
4. Type the extension after the pause(s).
5. Save the contact with a clear name, e.g. «Anna (Acme · Sales · ext 203)».

Next time you tap that contact, the phone dials the public number, waits the configured pause, then automatically sends the extension digits. You skip the menu, and you skip the queue if the extension is the only destination.

What if the extension does not answer?

A few practical options, in order of preference:

• Try a different extension: large teams usually have a fallback (e.g. press 0 for the operator).
• Send to voicemail: most cloud PBX platforms route unanswered calls to the user’s mailbox; leave a concise message with your name, number and reason for calling.
• Use the company’s main menu: yes, it is slower, but it gets you to a human. Ask the operator to connect you, and confirm the direct number for next time.
• Email or chat: many UK businesses now expose email, WhatsApp, or web chat as a fallback. Use those for non-urgent issues.

For compliance reasons, calls placed to a UK PBX extension via the public network are subject to the same UK GDPR and PECR rules as any other business call. If the call is recorded, the company must notify you at the start of the call.

Frequently asked questions about PBX extensions

Can I call a PBX extension from abroad?

Yes, as long as you can reach the company’s public number with international dialling. Use the pause + extension method, or save the number in international format (e.g. +44 800 123 4567,,203 for a UK company). Note that emergency call routing (999/112) is tied to the address registered on the SIP account, not to your physical location.

What is the difference between an extension and a DDI?

An extension is a short internal number that only works after you have reached the PBX (via the public number, a DDI, or DISA). A DDI (Direct Dial-In) is a real public number that rings a specific extension directly, without going through the main switchboard. DDIs cost the company a small monthly fee per number; extensions are free.

Can I reach a PBX extension on a mobile without installing anything?

Yes. The pause-and-extension method works with the native phone app on iPhone and Android, no softphone required. For a richer experience (presence, chat, video), install the provider’s softphone or use WebRTC in the browser.

How do I know the extension number of a person in a UK company?

Check the company website (many list extensions on the team page), the person’s email signature (e.g. anna@acme.com · 020 7946 0123 ext 203), or ask reception. Some companies expose a directory via their VoIP app.

Is calling a PBX extension free?

You pay the standard rate to reach the public number (free if it is a freephone 0800 / 0808 / 0500 number, normal UK landline rate for 01/02/03 numbers, mobile rate for 07 numbers). The extension is sent as in-band DTMF tones, so there is no extra cost for that part.

Do I need a softphone to call an extension on a smartphone?

No. The pause method works on the standard Phone app. A softphone (Zoiper, Bria, Linphone, or the provider’s own app) is only needed if you want to register as a SIP endpoint yourself. If you want to understand the SIP protocol behind this, read our SIP calls explained guide.

What happens if the extension changes?

The contact you saved stops working. Update the number in your phone with the new extension. This is one of the reasons many companies prefer DDIs: even if the extension changes, the DDI number can be re-pointed to the new user without changing the public number.

Are calls to UK PBX extensions subject to Ofcom rules?

Yes. The same Ofcom VoIP guidance applies: 999/112 emergency call handling, number portability, transparency on tariffs, and respect for the user’s right to a basic service. Cloud PBX providers in the UK are required to comply.

— Fonvirtual Editorial Team · Reviewed July 2026