Asterisk and FreePBX for a Small Office: Setup and Pitfalls

In short: should you run your own PBX

Asterisk is an open-source telephony engine, and FreePBX is a web interface on top of it. Together they give you extensions, IVR, queues, call recording and integrations with no per-user fee. The price of that freedom is administration: updates, monitoring and security. If nobody in the office looks after it, a cloud PBX is usually safer.

Installation options

• The official FreePBX distro or install script is the fastest path: OS, Asterisk and modules come in matching versions.
• FreePBX installed manually on Linux gives more control but a higher risk of version mismatches.
• Plain Asterisk with config files is for experienced admins: maximum flexibility, but everything lives in text files and the dialplan.
• A hosted VPS or an on-site server: a VPS suits remote staff, while an on-site server makes sense with analog lines or strict rules on where recordings are stored.

For 10 to 50 extensions, a modest server or VM is enough. Recording every call, codec transcoding and conferences need more resources.

SIP trunks

A trunk is the connection to your carrier that carries external calls. Configure it with PJSIP: the legacy chan_sip driver is no longer supported in current Asterisk versions.

When connecting a trunk, check:

1. The carrier's auth method: registration with username/password or IP-based trust.
2. Number formats for inbound and outbound calls (with or without country code).
3. Supported codecs, so you avoid unnecessary transcoding.
4. NAT settings: external address, local networks and the RTP port range on your firewall.

"The call connects but there is no audio" or "audio only one way" is almost always a NAT and RTP problem.

asterisk -rvvv
pjsip show registrations
pjsip show endpoints

These commands show whether the trunk is registered and which phones are online.

Extensions, IVR and queues

• Extensions: plan a numbering scheme up front (for example, departments by hundreds) and use long random secrets for every extension.
• IVR: keep menus short, 3 to 4 options plus a way to reach a person. Record greetings at a calm pace.
• Queues and Ring Groups: a queue suits sales or support with hold music and stats; a ring group is for simple "ring everyone".
• Time Conditions: separate business hours from after hours, or night calls will land in an empty queue.

Call recording

Recordings fill disks fast. Decide in advance:

• how long to keep recordings and who can access them;
• where to move older files: a NAS, object storage or your CRM;
• how to notify callers about recording in line with local law.

Set up automatic cleanup or archiving, or one day a full disk will stop the PBX.

Protecting against SIP fraud

A compromised PBX can place many expensive international calls overnight on your account. The minimum set of measures:

• Do not expose SIP to the whole internet: allow only your carrier's IPs and use VPN for remote staff.
• Strong secrets for every extension, never matching the extension number.
• Fail2ban or the FreePBX Responsive Firewall to block brute force.
• Restrict outbound routes: block international destinations you do not need, or protect them with a PIN.
• Carrier-side limits on balance and concurrent calls.
• Regular updates of Asterisk, FreePBX and modules.

When a cloud PBX is wiser

• There is no admin and no budget for ongoing support.
• Staff mostly work remotely.
• You need availability guarantees without your own standby server.
• You have few extensions and no complex call routing.

Your own PBX wins when you need deep CRM integrations, custom call logic, full control over recordings or many users.