Internet with guaranteed speeds and up-time. Your best effort internet (cable, fiber optics). Fixed wireless is guaranteed speed and up-time on roof implementation.
You can manage your entire phone system from your desktop computer. It is easy to add and change users, assign phones, manage extensions and groups anytime from anywhere in the world. Auto attendants and ringing a desk phone and cell phone simultaneously is simple.
Software-Defined WAN also has the advantage of removing potentially expensive routing hardware by provisioning connectivity and services via the cloud.