RingEX

No need to have anything but a desk phone, computer, or mobile device, and the internet to make it work. It is very feature-rich. They work with many phones, even others like Microsoft say are not compatible. If you have a bunch of old equipment that won't work with another cloud provider, RC will be one of your best bets to work with your hardware. If even they don't work with your devices, you probably need to get rid of your archaic technology. Provision is very quick and easy. Their chat support has less than a 10-minute wait, usually no wait. Their support is very capable. They handle all firmware upgrades automatically, at least with our VVX phones.

Cost much more than a locally-hosted system but I think if money is not an issue, it's much better to let your company do what it does best, and let RC do what it does best. Don't try to be a VoIP provider company just for yourselves. Let the pros do it (unless if you're a VERY large company maybe).
Don't pay crazy more for phones from them, just buy them on Amazon and provision them yourself in about three minutes. For rare, advanced problems, sometimes their support drops the ball and you need to contact your account manager. Sometimes he'll be out of the office for several days though. Anytime we've had more than two phones down, they have been able to solve our problems by the next morning, even for CRAZY issues. Most of the time support is very great and I recommend it.

I liked the ability to access our phone system remotely, but this is no longer a novel tech setup.

As a business, we were assigned one [SENSITIVE CONTENT] who was incredibly difficult to reach. When attempting to seek out additional assistance as the number given to us was no longer able to reach her, we were told only she would be able to assist us - that we should try emailing once again. As we don't have an abundance of free time with which to chase down our representative, this proved to be frustrating and not at all convenient.

RingCentral allowed our office to keep it's dedicated Canadian office phone number and take that office phone global with it's VoIP system.

We we're able to use text authentication services, call clients, and keep our office going from any location in the world.

RingCentral offers more than most VoIP services - mainly because of it's dedicated app. That said the cost of this service is far more than most of it's competitors.

It's an expensive solution unless easy of use outweighs cost.