3CX is a software phone system for businesses, developed by the company of the same name since 2005. It is built on the SIP standard and on WebRTC: it handles extensions, numbers and the SIP trunks of your VoIP provider, call queues, ring groups, the auto attendant (IVR) and office hours, and it delivers calls to IP phones, the browser and the Android and iOS apps.
Beyond voice, 3CX brings video calls, website live chat and WhatsApp messages into the same console, and it integrates with CRMs such as Salesforce, HubSpot and Zoho, with Microsoft 365 and with Google. You can run it hosted by 3CX, on premise on a server in your office, or self-hosted on a cloud server: the 3CX VPS is that third option, with the PBX on a machine of your own in Italy.