Traditional phone systems tie you to physical lines, per-extension hardware and an engineer visit for routine changes. An IP PBX runs telephony over the data network you already maintain, which changes both the economics and what the system can do.
How it differs
Calls become data. Handsets connect over Ethernet — usually powered by PoE, so no separate power supply at each desk — and external calls route over SIP trunks from a provider rather than analogue or ISDN lines. The PBX itself may be an appliance on site or software on a server.
Practical consequences: one cabling system instead of two, extensions that can be added or moved in software, and a phone that works the same way from a branch office or a laptop at home.
Where the savings come from
- Line rental. SIP trunks are typically materially cheaper than an equivalent count of traditional lines, and you buy concurrent channels rather than physical lines.
- Internal and inter-site calls. Traffic between your own sites travels over your network at no per-minute cost.
- Moves and changes. Reassigning an extension is a configuration change, not a site visit.
- Cabling. One structured cabling system serves both data and voice.
Features that used to be expensive
Capabilities that once required costly add-ons are now standard on most IP PBX platforms: auto-attendant menus, ring groups and hunt lists, voicemail delivered to email, call recording, queues with reporting, conferencing, presence, softphones and mobile apps, and CRM integration so a call arrives with the customer record attached. For any business that handles inbound enquiries, the queue statistics alone often justify the change.
What the network must deliver
Voice is unforgiving about network quality in a way that file transfers are not. Before deployment, confirm:
- QoS configured on switches and router so voice packets take priority over bulk traffic.
- Bandwidth for the number of concurrent calls, with headroom — roughly 100 kbps per concurrent call with common codecs, plus overhead.
- Latency, jitter and packet loss within limits. Jitter and loss cause the choppy audio users complain about; a jitter buffer helps but does not fix a poor link.
- PoE capacity on the switches for the handsets, with UPS backing so phones survive a power cut.
- Internet resilience. If the connection is your only path to the outside, plan a failover — a second circuit, or automatic diversion to mobiles.
Where the network is not ready, fixing it first is far cheaper than debugging call quality afterwards.
Security
An exposed, badly configured PBX is a target for toll fraud, and the bills can be severe. Sensible baseline: strong unique passwords on every extension (never leave defaults), disable unused features, restrict SIP registration by IP where practical, put international dialling behind explicit permission or a PIN, set spend limits with your provider, and keep firmware current. Place the PBX behind a firewall configured for SIP rather than on an open public address.
Migrating without disruption
A staged approach avoids the classic cut-over disaster:
- Audit current extensions, call flows and numbers, and confirm what genuinely needs to be preserved.
- Verify the network — test QoS and capacity before any handsets arrive.
- Run in parallel where possible, moving a department at a time.
- Port main numbers only once the new platform is proven; keep the old lines briefly as fallback.
- Train users on the handset and on the features they will actually use — most disappointment comes from features nobody was shown.
On-premise or cloud?
On-premise gives control and keeps working during an internet outage for internal calls, at the cost of hardware and maintenance. Cloud-hosted removes the hardware and scales easily, but depends entirely on connectivity. Where internet reliability varies, an on-premise or hybrid platform is often the more dependable choice.
TSB Smart Tech supplies, installs and configures IP PBX and VoIP telephony — including the structured cabling and network it depends on. Talk to us about migrating your phone system.