Before you can start considering a brand, you need to figure out exactly how you want your business to use a phone system. Look at your existing phone system and decide whether you're going to simply keep all of it and bolt some VoIP functionality on top, retain only part of it, or replace the whole thing. Frequently, a total replacement isn't in the cards if only because some parts of your existing phone system can't be easily changed over to softphones or even desktop VoIP handsets.
“Hi, you’ve reached [your name] at [your company]. I’m unavailable right now — probably helping [type of company] get [X results, e.g. ‘double their leads in 60 days,’ ‘hire the best and brightest engineers,’ ‘convert 40% more customers.’] Leave your name and number, and we’ll discuss how your company can see similar results.” “Hello, this is [your name] at [company]. Thanks for calling. Please leave your name, number, and reason you’d like to chat, and I’ll get to back to you ASAP.” “Hi, you’ve reached [name] at [company]. If you need a quick response, please shoot me an email at [insert email address] and I’ll be in touch by EOD tomorrow. If it’s not urgent, leave me a message with your name and number. Have a great day.” “Hey, this is [your name]. If you’re calling for [X reason], please [contact so-and-so] or [go to our website, send me an email]. For all other inquiries, leave your name and a brief message and I’ll call you back within [one, two, three] business day[s].” “Hello, you’ve reached [name] at company. I’m unable to come to the phone right now. Leave your name and number, and I’ll return your call as soon as I’m free. Thank you.”

25. "Hello! Thanks for reaching out to [company]. We're closed today for the holiday, and will reopen tomorrow. If you leave your name, number, and a brief message, we'll give you a call when we're back in the office. Thanks again, and have a great day."
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.