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.
This is a tough category because all telephone service companies have complaints on public forums. Remember that people who comment on these forums are more likely to be unhappy with the service, while happy people don't frequently take to publicly announcing their happiness with a product. Acknowledging that all the companies we looked at have some complaints, the winner for best service is Vonage, one of the first phone companies to offer VoIP for business.

Pricing: MightyCall plans start at $19.99 per month, offering 1000 minutes and 2 toll-free numbers. Their largest plan is $99.99 per month and features 15,000 monthly minutes, 10 toll-free or local numbers, call recording, voice to text, API access, and softphone usage.
Creating a voicemail message, particularly for business, is as important to your brand as your business card, email, letters, signage etc. It is imperative the prospective client can confirm they called the right business. Leaving a voicemail is even more important. It is a conversation starter.