Adding and managing extensions in 3CX
How to add extensions in 3CX, set roles and permissions, and get new staff up and running quickly.
Extensions are the heart of your 3CX system: each one is a person (or a phone, or a meeting room) that can make and take calls. Get the structure right at the start and onboarding a new staff member is a five-minute job; get it wrong and you end up with duplicate numbers, broken voicemail and people who can dial international when they shouldn't.
This guide covers how to add extensions in 3CX, set sensible roles and permissions, and get a new starter dialling quickly. It is conceptual on purpose — exact menu labels shift between versions, but the ideas hold whatever build you are on.
What an extension actually is
In 3CX an extension is a numbered identity in the Admin Console that ties together a short internal number (say 100, 101, 102), a user who logs in to the Web Client and the apps for Windows, Mac, iOS and Android, the devices that register against it, and settings like voicemail and outbound permissions.
One person does not need one phone. A single extension can ring a desk phone, the desktop app and the mobile app at once, so a call follows the person, not the hardware. New to the platform? Our plain-English guide to 3CX is a good primer.
Plan your numbering first
Spend ten minutes on a numbering plan before you create a single extension. It saves a lot of re-work.
- Pick a length: three digits (100–199) suits most small offices; four digits give you room to grow.
- Reserve blocks by team — 1xx for sales, 2xx for support, 3xx for the warehouse — and leave gaps so new people slot in near their team.
- Keep short numbers like 0 or 9 clear, since outbound dialling often uses a leading digit.
Numbering also feeds into inbound and outbound rules, which map a published number (a DID) to the right person or group.
Adding a new extension
Adding an extension follows the same shape every time:
In the Admin Console, create a new extension and give it a number from your plan.
Enter the person's first name, surname and email. The email matters — 3CX uses it for the welcome message, app login and voicemail-to-email.
Let 3CX send the welcome email. It carries the QR code and links the person needs to set up the Web Client and mobile app themselves, far quicker than configuring each device by hand.
Choose how they'll take calls — a provisioned desk phone, the desktop app, the mobile app, or a mix. For desk phones, see our guide to provisioning IP phones.
Set voicemail, business-hours behaviour and ring time, then save.
That's a working extension — the new starter can be making calls within minutes, often before the desk phone arrives, using the Web Client in any browser.
Roles and permissions
3CX uses roles to decide what each user can see and do, and getting them right is the difference between a tidy system and a security headache. Most staff only need a basic user role, which manages their own status, forwarding and voicemail. Give team leaders a manager role so they can see and report on their team. Keep the full System Owner / Admin role to one or two people — every admin login is a potential way in for an attacker.
Just as important are outbound calling permissions. Locking down international and premium-rate dialling on extensions that never need it is one of the simplest steps against toll fraud — the scam where a compromised extension racks up thousands in overseas calls overnight. Our guide on securing 3CX against toll fraud covers the rest.
Grouping extensions and onboarding cleanly
Most businesses route incoming calls to a group, not one person. Use a ring group when several phones should ring together for a small sales or reception team, or a call queue when volume is higher and you want callers held in order with a polling strategy such as Round robin or Longest waiting. Assign extensions to groups as you create them.
A few habits keep things healthy as staff come and go. For new starters, create the extension, let the welcome email do the heavy lifting, add them to the right groups, and check their outbound permissions match their role. For leavers, disable the extension rather than deleting it, so voicemails aren't lost, then redirect their DID and remove them from queues.
None of this is hard, but it adds up across a busy office. If you'd rather have it set up properly from day one, SIP Connect can do the lot — we're a family-run Melbourne telco that installs and supports 3CX phone systems for Australian SMEs, on a hosted PBX or your own server. Call 1300 747 266 or grab a free bill review.
What we see installing this in Melbourne
The most common mess on Australian SME sites is not the extension setup itself — it is what surrounds it. Consumer routers with SIP ALG quietly enabled will mangle registrations on the mobile app, so staff complain calls drop when they leave the office Wi-Fi. We turn ALG off at the gateway and re-test on the actual NBN service before signing off, because a cheap FTTN plan with 20 Mbps upload can sound fine on one extension and terrible when six are concurrent.
The other recurring issue is welcome emails landing in junk on Microsoft 365 tenants with tight anti-spoofing rules. We whitelist the 3CX FQDN before bulk-creating extensions, which saves a round of "I never got the QR code" calls.
Where we add value is the handover: walking reception through transferring to a mobile extension, locking down international dialling on warehouse handsets, and being on the phone the morning after cutover.
Frequently asked questions
How many extensions can I have in 3CX?
The practical limit is your 3CX licence and the simultaneous calls it allows, not the number of named people. Because 3CX is licensed on concurrent calls rather than per user, you can often add staff without extra cost — our 3CX licensing explained page covers how.
Can one person use a desk phone, the desktop app and their mobile at once?
Yes. A single extension can register multiple devices, so a call rings everywhere at once and you answer wherever you are.
What's the fastest way to get a new staff member dialling?
Create their extension with a correct email and let 3CX send the welcome email. They scan the QR code into the mobile app or log in to the Web Client and they're live in minutes — no desk phone needed to start.
Should I let everyone make international calls?
No. Restrict international and premium-rate dialling to the extensions that genuinely need it. It is the easiest guard against toll fraud and a surprise bill.
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