Hosted PBX vs SIP Trunks: Which to Sell and When

Both hosted PBX and SIP trunking replace what a legacy ISDN or analogue line used to do, but they solve the problem differently — and which one's right depends entirely on the customer in front of you. Here's a genuinely balanced look at both, so you can match the right option to the right business rather than defaulting to one every time.

The Core Difference

SIP trunking replaces the physical line connecting an existing on-site phone system (PBX) to the phone network, delivering that connection over the internet instead. The customer keeps their current PBX and handsets — only the connection method changes.

Hosted PBX replaces the phone system itself. There's no on-site PBX at all; the entire system runs in the cloud, with handsets, softphones and mobile apps connecting directly to it.

Side-by-Side Comparison

	SIP Trunks	Hosted PBX
On-site hardware	Keeps existing PBX	None needed — fully cloud-based
Upfront cost	Lower — no new system to buy	Lower per-seat, but may need new handsets
Ongoing cost	Per-channel pricing	Per-seat pricing, usually all-inclusive
Control & customisation	Full control retained over existing PBX configuration	Configured through the provider's portal
Remote & multi-site working	Depends entirely on the existing PBX's own capability	Built in as standard
Best suited to	Businesses happy with their current PBX, wanting the ISDN replacement done with minimal disruption	Businesses wanting to modernise fully, or without a PBX worth keeping

When SIP Trunks Make More Sense

• The customer has a recent, capable PBX they're happy with — no reason to replace working hardware.
• Minimal disruption matters more than new features — SIP trunking is typically the lower-friction migration path off ISDN.
• The business has specific PBX configuration built up over years that would be costly or risky to rebuild on a new platform.

When Hosted PBX Makes More Sense

• The existing PBX is old or already failing — there's little point connecting new SIP trunks to hardware that's on its way out anyway.
• Remote or hybrid working is a priority — hosted PBX handles this natively; retrofitting it onto an old on-site PBX often doesn't work well.
• The business is opening new sites or scaling quickly — hosted systems scale by adding seats through a portal, not by provisioning new hardware.
• The customer wants modern features as standard — call recording, mobile apps and auto attendants usually come bundled rather than bolted on.

The Margin Question

Neither option is straightforwardly "better margin" in every case — it depends on your pricing structure and the customer's channel count versus seat count. What matters more for margin, in practice, is fit: selling a customer the wrong option because it's what you always sell tends to create support overhead and churn, both of which cost more than the margin difference between the two products.

How Plustel Supports Both

Plustel offers wholesale SIP trunks and Cloud X, our own hosted PBX, both provisioned through the same Zeus partner portal and both running on our own switch rather than a resold third-party platform. That means whichever option fits a given customer, support and diagnostics stay in-house rather than being passed up a chain.

If you're not sure which fits a particular customer, our team can talk it through — and if the customer's still on ISDN, our ISDN switch-off guide covers the migration timeline in more detail.