Last updated 1 October 2026.
Hosted PBX is a phone system run by the provider and delivered as seats. SIP trunking supplies calling capacity to a PBX the customer already owns. UCaaS is a hosted phone system bundled with messaging, meetings and mobile. The technical differences are settled. The question a reseller actually has is which one to put in front of which customer.
Every guide ranking for these terms defines them accurately and then stops. This one maps them to customer situations, and to what each is worth to you in margin and support load.
The three, defined once
| Hosted PBX | SIP trunking | UCaaS | |
|---|---|---|---|
| What the provider supplies | The phone system itself, as a service | Calling capacity only | Phone system plus collaboration tools |
| What the customer keeps | Handsets and the network | Their own PBX, on premises or cloud | Handsets, apps and the network |
| Typical trigger | Ageing phone system, single or few sites | A PBX that still has useful life | Distributed staff, or several tools being replaced at once |
| Billing shape | Per seat | Per channel or per minute | Per user, usually tiered |
| Support load for you | Moderate | Lowest of the three | Highest, because the surface is wider |
| Revenue per customer | Middle | Lowest | Highest |
SIP trunking is the outlier. The other two compete with each other. SIP trunking competes with doing nothing, because the customer already has a working system and is replacing only the lines into it.
Which to sell to which customer
Sell SIP trunking when the PBX still has life in it
A customer who bought a PBX recently, or who has one that works and is still being depreciated, is not going to replace it because you would prefer the seat revenue. Offering trunks respects the investment, gets you into the account, and gives you the relationship for when the system does reach end of life.
This is the least profitable of the three and often the most strategic. Treat it as a way in rather than as the deal.
Sell hosted PBX when they want phones, not a project
Single site or a few sites, staff mostly in one place, a phone system that has become a liability, and no appetite for changing how people work. Hosted PBX replaces the box with a service and changes almost nothing else. Price-sensitive customers land here, and trying to move them up the stack usually stalls the deal.
Sell UCaaS when more than the phone system is being replaced
Distributed or hybrid staff, several disconnected tools for calling, messaging and meetings, or a customer already paying for a collaboration suite alongside a separate phone system. UCaaS earns its higher price by consolidating, and if nothing is being consolidated the customer will experience it as a more expensive phone system.
What none of the three solve
A genuine contact centre, with queues, workforce management and reporting on agent performance, is CCaaS and a different product. Selling UCaaS into a contact centre requirement is the most common mis-sell in this category. Some UCaaS platforms include light queueing, which is not the same thing and should not be presented as if it were.
A decision path that survives contact with a customer
- Does the customer own a PBX with useful life remaining? If yes, lead with SIP trunking.
- Are staff mostly in one place, and is the requirement just working phones? If yes, hosted PBX.
- Are staff distributed, or are messaging and meetings being bought separately today? If yes, UCaaS.
- Is there a queue, an agent supervisor, or a service-level target on answering? That is CCaaS. Refer it or partner for it.
The order matters. Asking about the existing PBX first prevents proposing a replacement to somebody who cannot buy one this year.
What this means for your own margin
The three models produce different businesses, not just different products. A book of SIP trunking customers is low-touch, low-revenue and relatively easy to lose to price. A UCaaS book is higher revenue with a support burden attached, and it is far harder for a competitor to unpick because the customer’s daily work is inside it.
Neither is the correct answer. What is worth avoiding is drifting into a UCaaS book while still resourced for trunking, which is how support quality drops at exactly the moment revenue grows.
Where RingLogix is the wrong choice
If the account you are chasing is a contact centre requirement, or the customer wants to keep and operate their own PBX indefinitely with only the cheapest possible capacity behind it, we are not the right supplier for that deal. A carrier selling raw termination will beat us on the second, and a CCaaS specialist will beat us on the first.
Frequently asked questions
What does hosted PBX mean?
The private branch exchange, the system that routes calls inside an organisation, runs in the provider’s data centre rather than on the customer’s premises. The customer gets phones and features as a service and does not maintain the hardware.
Is PBX the same as VoIP?
No. PBX describes the call-routing system. VoIP describes carrying calls over IP rather than traditional lines. A PBX can be on premises or hosted, and either can use VoIP. The terms answer different questions, which is why they get confused.
Is SIP trunking the same as VoIP?
SIP trunking is one way of delivering VoIP. VoIP is the broad category of voice over IP; SIP trunking is the specific arrangement that connects a PBX to a provider’s network using SIP. All SIP trunking is VoIP, but plenty of VoIP is not SIP trunking.
What is the difference between hosted PBX and UCaaS?
Hosted PBX is the phone system delivered as a service. UCaaS is that plus messaging, meetings, presence and mobile in one platform. In practice the line has blurred, because many hosted PBX products now include some of those features. Compare what is actually in the tier being quoted rather than the label on it.
What are the three types of PBX?
Traditional on-premises PBX using circuit-switched lines, IP PBX which is on premises but carries calls over IP, and hosted or cloud PBX operated by a provider. The middle one is what SIP trunking most often connects to.
Which is cheaper, SIP trunking or hosted PBX?
SIP trunking is usually cheaper per month for a customer who already owns a working PBX, because they are buying capacity rather than a system. It stops being cheaper once the PBX needs replacing, since the cost of the replacement lands in one year. Compare over the expected life of the system rather than monthly.
Deciding
The reseller question is not which of the three is best, since none of them is. It is which one matches the customer in front of you and which kind of book you want to be running in three years. Ask about the existing PBX before quoting anything, and the rest of the conversation arranges itself.
If you are working out which of the three to build a practice around, the RingLogix partner programme covers how each is packaged, and our piece on wholesale versus retail SIP trunking goes deeper on the capacity side.
