What Is a Hosted PBX?
A Hosted PBX (Private Branch Exchange) is a complete cloud phone system. The "PBX" — the brains of the operation — lives in a data centre, not in your office. You get:
- Extensions for every staff member
- Auto-attendant / IVR menus
- Ring groups (ring multiple phones at once)
- Voicemail to email
- Call transfer, hold music, call queues
- A softphone app for desktop and mobile
You pay per user per month. No server to buy or maintain. The provider handles all upgrades, redundancy, and backups.
What Is a SIP Trunk?
A SIP Trunk is a virtual phone line that connects an existing on-premise PBX (such as 3CX, Asterisk, FreePBX, or a legacy PABX) to the public telephone network via the internet.
Think of it as replacing your old PSTN or ISDN lines with internet-based lines. Your existing PBX hardware stays in place; the SIP Trunk gives it a path to make and receive calls.
You purchase SIP channels (simultaneous call paths) rather than per-user licences. 10 channels = 10 simultaneous calls, regardless of how many extensions your PBX has.
Key Differences at a Glance
| Factor | Hosted PBX | SIP Trunks |
|---|---|---|
| Existing PBX needed? | No | Yes |
| Upfront hardware cost | Phones only (optional) | Existing server stays |
| Pricing model | Per user/month | Per channel/month |
| IT management needed | Minimal | PBX admin required |
| Best for | New or growing businesses | Businesses with existing PBX |
| Disaster recovery | Built-in | Failover to mobile included |
When to Choose Hosted PBX
- You are starting fresh with no PBX hardware
- You want a fully managed system with zero on-site servers
- Your team works from multiple locations or remotely
- You want to add or remove users without an IT project
- You need features like call recording, IVR, and call flows without paying for hardware licences
When to Choose SIP Trunks
- You have an existing PBX investment (3CX, Asterisk, Mitel, etc.) you want to keep
- Your current ISDN or analogue lines are being disconnected (NBN migration)
- You have an IT team who manages your phone system
- You make a very high volume of calls and channel-based pricing is cheaper at scale
- You need advanced PBX features your current hardware already provides
Cost Comparison: 20-User Business
For a 20-person Perth business with 6 simultaneous calls:
- Hosted PBX: 20 users × $20.90 = $418/month. No on-site server maintenance.
- SIP Trunks (existing 3CX): 6 channels × $29.95 = $179.70/month + existing 3CX licence cost. Lower monthly outlay but requires PBX server maintenance.
If you already own and are happy with your 3CX system, SIP Trunks will almost always be cheaper. If you are starting fresh, Hosted PBX eliminates the $2,000–$5,000 3CX server and licence cost.