Glossary / PBX Systems
🏢 PBX Systems covers the different types of business phone systems available today, from traditional hardware in your server room to cloud-hosted platforms you access through the internet. This section contains 16 terms.
On this page: PBX · Cloud PBX · IP PBX · Hosted PBX · On-Premises PBX · Virtual PBX · Hybrid PBX · Multi-Tenant PBX · PBX Appliance · Open-Source PBX · Asterisk · FreePBX · FusionPBX · FreeSWITCH · 3CX · UCaaS
PBX (Private Branch Exchange)
A private phone system used within a company. It connects internal phones to each other and to the outside telephone network. A PBX lets employees call each other using short extension numbers and share a limited number of external phone lines. Without a PBX, every employee would need their own direct phone line from the phone company.
Cloud PBX
A phone system hosted entirely in the cloud (on remote servers managed by a provider). You do not install or maintain any phone system hardware. Your phones connect to the provider over the internet. The provider handles all updates, backups, and maintenance. Cloud PBX is the fastest-growing type of business phone system because it is flexible, scalable, and requires no upfront hardware investment.
Related: Hosted PBX · UCaaS · SIP Trunking
IP PBX
A phone system that uses internet protocol (IP) to route calls instead of traditional circuit-switched connections. An IP PBX can be a physical server in your office or a virtual machine. It manages calls over your local network (LAN) and connects to the outside world through SIP trunks. IP PBX systems offer more features than traditional PBXs, including voicemail-to-email and call recording.
Related: PBX · On-Premises PBX · SIP Trunking
Hosted PBX
A PBX system that runs on servers owned and managed by a third-party provider, not in your office. "Hosted PBX" and "Cloud PBX" are often used interchangeably today. Technically, a hosted PBX may run on a dedicated server for your company, while a cloud PBX usually runs on shared infrastructure. In practice, the difference is minimal for most businesses.
Related: Cloud PBX · Multi-Tenant PBX · ITSP
On-Premises PBX
A phone system physically installed at your business location. You own the hardware, manage the software, and are responsible for maintenance and updates. On-premises PBX gives you full control over your phone system but requires IT expertise and capital investment. It is becoming less common as businesses move to cloud solutions.
Related: IP PBX · PBX Appliance · Hybrid PBX
Virtual PBX
A lightweight phone system that provides basic call management features (call forwarding, voicemail, auto attendant) without a full PBX installation. Virtual PBX services are entirely cloud-based and often aimed at very small businesses, freelancers, or sole traders who need a professional phone presence without complex infrastructure.
Related: Cloud PBX · Auto Attendant
Hybrid PBX
A phone system that combines on-premises hardware with cloud services. For example, a business might keep its existing IP PBX hardware but route some calls through a cloud service for remote workers. Hybrid setups are common during transitions from legacy systems to full cloud deployments. They let businesses move gradually without replacing everything at once.
Related: On-Premises PBX · Cloud PBX · SIP Trunking
Multi-Tenant PBX
A single PBX system that serves multiple separate companies at the same time. Each company (tenant) gets its own isolated environment with its own extensions, settings, and phone numbers. Cloud PBX providers typically use multi-tenant architecture to serve thousands of customers from the same platform efficiently.
Related: Cloud PBX · Hosted PBX
PBX Appliance
A pre-built hardware device that runs PBX software out of the box. You plug it in, configure it through a web browser, and it is ready to handle calls. PBX appliances are popular with small and medium businesses that want on-premises control without the complexity of building a server from scratch. Examples include devices from Innovaphone and Yeastar.
Related: On-Premises PBX · IP PBX
Open-Source PBX
A phone system built on software whose source code is freely available for anyone to use, modify, and distribute. Open-source PBX platforms are free to download, but you need technical skills (or a paid consultant) to install, configure, and maintain them. They offer maximum flexibility and customisation.
Related: Asterisk · FreePBX · FreeSWITCH · FusionPBX
Asterisk
The most widely used open-source PBX software in the world. Created in 1999 by Mark Spencer, Asterisk turns a standard Linux computer into a full-featured phone system. It supports SIP, traditional phone lines, and hundreds of telephony features. Many commercial PBX products (including FreePBX and some Cloud PBX platforms) are built on top of Asterisk.
Related: Open-Source PBX · FreePBX · SIP Protocol
FreePBX
A free, open-source web interface for managing Asterisk. FreePBX makes Asterisk easier to use by providing a graphical dashboard where you can configure extensions, call routes, voicemail, and IVR menus without writing configuration files manually. It is maintained by Sangoma Technologies and has a large community of users worldwide.
Related: Asterisk · Open-Source PBX · IVR
FusionPBX
A free, open-source web interface for FreeSWITCH. It provides a graphical management panel for building multi-tenant phone systems, call centres, and voicemail platforms. FusionPBX is used by service providers who want to offer hosted PBX services to multiple customers from a single server.
Related: FreeSWITCH · Open-Source PBX · Multi-Tenant PBX
FreeSWITCH
An open-source telephony platform designed for high-performance, carrier-grade deployments. Unlike Asterisk, which started as a PBX, FreeSWITCH was built from the ground up as a media server and soft switch. It handles large volumes of concurrent calls efficiently and is used by VoIP service providers, conference platforms, and large enterprises.
Related: FusionPBX · Open-Source PBX · Softswitch
3CX
A commercial PBX software platform that can run on-premises, in your private cloud, or as a hosted service. 3CX offers a free tier for small deployments and paid licences for larger organisations. It provides a web-based management console, mobile apps, video conferencing, and live chat. 3CX is popular with businesses that want a modern phone system with an easy interface.
Related: IP PBX · Cloud PBX · Competitors
UCaaS (Unified Communications as a Service)
A cloud-delivered platform that bundles voice calling, video conferencing, team messaging, file sharing, and sometimes contact centre features into a single subscription. UCaaS goes beyond a simple Cloud PBX by integrating multiple communication tools. Providers like Microsoft Teams, Cisco Webex, and Mixvoip offer UCaaS solutions.
Related: Cloud PBX · Microsoft Teams · Cisco Webex
Related Sections
🔗 Core Telephony Concepts — PSTN, ISDN, DID, and other foundational terms
🌐 VoIP Fundamentals — Voice over IP, softphones, WebRTC, and packet switching
📡 SIP Trunking — How your PBX connects to the outside phone network
🔧 Deployment and Infrastructure — Failover, redundancy, and network setup
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