In spite of the "cloud" is a trending word today, it doesn't always work well for large companies. Why? Imagine an office building with a thousand of employees. If a hundred of those folks simultaneously talk to each other over the phone, they would need 90 Kb/s x 100 = 9 Mb/s guaranteed throughput. 9 Mb/s doesn't mean much for a local ethernet, but it's quite a significant amount if your company just has a 100Mb/s internet connection to the outside world. The 1/10th of your total bandwidth would be wasted.
The second answer is integration. It is much easier to integrate a PBX with a server running your existing applications if both are located at the same place. No need to use external IPs, configure firewalls, etc.
Some companies just have their policies that do not allow to store any customer-related information, including phone calls, outside.
If one or more "no cloud" answers applies to your business, how can EntrCom help you? We offer state of the art PBX servers designed and built by our engineers from the most reliable parts. EntrCom makes PBX servers equipped with redundant power supplies and redundant drives, including hot spares. We also offer UPS-equipped solutions for unparalleled reliability. Our specialists thoughtfully test the equipment and software to ensure every single component will be able to withhold heavy loads exceeding the standard work requirements.
We also always leave room for an upgrade if you need to add more capacities in the future. If your company has overgrown your PBX, we can replace the existing box. Grown too big? Not a problem. We offer load-balanced solutions with an evenly distributing voice transcoding among multiple PBX boxes, with a centralized and mirrored database. Fault tolerance is our priority.