Great list! These are the new generation of telecommunications. We are witnessing the transition from desk phone to mobile first communications. Apps are beginning to run all business phone systems. We all have a smartphone, we are always on the go and we want to cut the cord. Another fantastic new service is Vocaly.io run by three seasoned and well know telecom insiders. My company Compati Home Healthcare uses them and it is a great service.
To begin with, it provides clients with toll-free and vanity phone numbers. From there, users get additional call management features, such as call forwarding, advanced routing, blocking, and screening. Users can also forward calls internationally, set up voicemail, and replace a full-time receptionist with an auto-attendant. Meanwhile, the conferencing option allows for both audio and video calls.

Business voicemail greetings are rarely thought of as a prime way to connect with customers. But just because you're not available doesn't mean you can't make a positive impression on your customers when they reach your voicemail box.
Lines and extensions: With an analog phone system you might, for example, pay your telco for two or four lines to allow your business to have that many simultaneous phone calls. For that to work, you'd need a two- or four-line analog business phone system, which are some of the most common analog systems on the market.