Generally speaking, you'll find that the benefits of data network services such as VoIP and SIP are far greater than PRI lines because you have less dedicated hardware and there are more providers to choose from.
Voicemail is a voice message that a caller leaves when the person called is absent or is busy with another conversation.

As a business owner, you want every customer interaction to leave a lasting impression. But have you ever stopped to ask yourself how your customers feel about your business voicemail greeting?
In practice, most businesses are simply handling this on a case-by-case basis since COVID is a temporary problem. Most home networks can handle the extra load as long as the employee makes sure that other latency-sensitive traffic, like gaming or video streaming, is kept to a minimum during the hours when they need to talk. If some home routers develop problems, IT staff simply build a queue and handle those one at a time. Sometimes they'll be able to access the router remotely with the employee's permission, sometimes they'll have to walk that employee through configuration steps to fix the problem. Sometimes the employee will just have to live with it unless the company springs for a new router or a higher bandwidth tier from the employee's ISP.