A business eSIM is a digital SIM that delivers a complete business phone system — auto-attendant with custom greeting, working-hours routing, voicemail with email-delivered transcripts, call recording, call forwarding, hunt groups, IVR menus, and departments — on the cellular voice network, instead of as a softphone app.
The line rings on your phone's native dialer like any cellular call. The call-handling features run server-side; the device runs no extra software for calls. The mobile app is a control panel for configuring the system, not the place calls happen.
Business eSIMs are sold by telephony providers (Kelir is one example) as a monthly subscription. They are unrelated to travel eSIMs (Airalo, Holafly — short-term data plans abroad on someone else's number) and structurally different from softphone-based business phones like Quo, Grasshopper, Dialpad, or Google Voice. Same call-handling system feature set as those softphone tools; different delivery model.