ECL has worked with and installed many office PBXs over the years -- Panasonic hybrids, Microsoft Response Point, Nortel, …, etc. All of the above had gone south. Many other PBXs still left in the market are not doing so well.
We had been looking to replace our business PBX offerings with one that has longevity and will never be dropped by the vendor. Alas, we have found it -- the open source Asterisk: https://en.wikipedia.org/wiki/Asterisk_(PBX)
Over the past 2 years, we have been upgrading our customers' existing 3CX PBXs with great success. We are now upgrading all other brands of PBXs as we have figured out a way to smoothly and inexpensively transition most brands of PBXs to Asterisk.
For those who are still using cloud PBXs, which are generally unreliable, lacking in features, or too expensive to operate, we recommend setting up your Asterisk PBXs in your own local cloud.