[Blind-sysadmins] accessible phone systems

Hi all, The company I work for has a very old Mitel phone system, and we're starting to look at upgrading to a modern phone system that's managed in the cloud. Has anyone had experience with modern phone systems, and can comment on which are or are not accessible? Mainly asking in terms of administration and soft phone applications. The options we're currently looking at are Windstream and Harbor Cloud, but are also open to other suggestions. Thanks, Mike