After a merger, we were on a Cisco on-premise system as well as a proprietary phone system. We needed to put both companies onto the same unified system. We knew we didn't want another Cisco system as they are extremely difficult to work with (both as a product and a company). I pitched RingCentral to our company as a solution that would 100% work, guaranteed. I had implemented it at a previous company and knew it would work. The other staff wanted to try out Teams Calling and Skype for Business. I let them fail at that first, sometimes you just have to let people fail until they admit you were right all along.
After the failures to implement Teams/Skype, I was given the go-ahead to try out RingCentral on a test basis. I knew it would work, and of course it did. Once you're on a 100% cloud system, you'll never go back to on-premise. I implemented RingCentral and any hiccups I ran into due to call routing or desk phone (99% of our users don't have a desk phone, but a few wanted one) setup, support was very helpful if I couldn't figure it out from the online support. We have been using it solidly for 8 months now without issues.
The cell phone and desktop app are easy enough to figure out that you don't need to train your users. And if you can help people see the light that they don't need a desk phone anymore, that will greatly simplify the implementation. A large graphical UI is the easiest thing to figure out as compared to a small screen with a bunch of physical buttons, so users can learn on their own.
I'll never have to worry about upgrading some on premise piece of junk again. I'll just give RingCentral my credit card each month and know my phone system is going to work 24/7 without any maintenance on my part.
I am the finance guy implementing the phone system. I'm not the tech guy here. If I can do it, it must be so simple anyone can do it.