[Glossary](https://telxpress.com/glossary/) / Phones # PBX A **PBX** (private branch exchange) is a business phone system that switches calls between internal extensions and the outside world; it can be a box on your premises or a hosted service in the cloud. - Phones - Updated October 11, 2026 - Written by the Telxpress advisory team 01 In depth ## What it is, why it matters and *what to ask a vendor* A PBX gives a business many extensions behind a few outside numbers, with features such as transfers, hold, voicemail, auto attendants and ring groups. Traditional PBXs were hardware in a closet connected to carrier lines. IP PBXs connect over the network and SIP trunks; hosted or cloud PBXs run in the provider's data center as a service. For a growing business the question is rarely whether to have a PBX but where it should live. On-site systems give control and keep internal calls working during an internet outage; hosted systems remove hardware, scale per user and connect easily to AI agents and CRMs. Many businesses run a hybrid during a transition. Ask a vendor how long the system is supported with security updates, how remote and mobile workers connect, what it costs to add a location, how E911 reports the caller's location from each phone, and how call recording and AI features are added. If the PBX is more than a few years old, ask for a migration path rather than a repair quote. 02 Related terms ## Terms that usually come up *alongside it* - Phones ### [SIP trunk](https://telxpress.com/glossary/sip-trunk/) A SIP trunk is a virtual phone line delivered over the internet that connects your own phone system (an on-site or hosted PBX) to the public telephone network, replacing traditional analog or digital carrier lines. - Phones ### [Cloud phone system](https://telxpress.com/glossary/cloud-phone-system/) A cloud phone system is a business phone service hosted by a provider and delivered over the internet, so phones, apps and features are managed through a web portal rather than hardware in your office. - Phones ### [UCaaS](https://telxpress.com/glossary/ucaas/) UCaaS (unified communications as a service) is a cloud subscription that combines business phone calling, video meetings, team messaging, voicemail and often contact-center features in one platform managed by the provider. - Phones ### [E911](https://telxpress.com/glossary/e911/) E911 (enhanced 911) is the emergency-calling capability that sends a caller's phone number and location to dispatchers; for business phone systems, Kari's Law and RAY BAUM's Act set specific federal requirements. 03 At Telxpress ## Where this shows up *at Telxpress* The pages and articles where this term does real work: what we advise, build and support. - Page ### [Business VoIP & Cloud Phone Systems in Irvine](https://telxpress.com/solutions/business-technology/phone-systems/) VoIP, cloud phone systems, UCaaS and SIP trunks from Yealink, Nextiva, Avaya, Yeastar and Polycom, installed, supported and ready for AI call handling. - Article ### [Boosting Productivity: How Cloud-Based Phone Systems Change Business Communication](https://telxpress.com/insights/boosting-productivity-how-cloud-based-phone-systems-revolutionize-business-communication/) What moving call handling from a box in the closet to a hosted platform does for mobility, scaling, customer service, continuity and your IT team's time. - Page ### [About Telxpress: Irvine Business Solutions & AI Advisors](https://telxpress.com/about-us/) Why a telecom company became an AI advisor: our history, what we do, the Orange County area we serve, our partners and the values we work by. Next step ## Want This Applied *to Your Business?* Book a free 30-minute AI readiness consultation. You'll leave with three AI opportunities specific to your business, whether you work with us or not. [Book My Free Consultation](https://telxpress.com/book/) [Take the Free AI Readiness Assessment](https://telxpress.com/ai-readiness/) [Or call 24/7: (949) 861-4500](tel:+19498614500) Last reviewed: October 11, 2026. Published by Telxpress, Irvine, CA.