Remote working is great but let's not forget there are places that still require zone or building wide paging like schools or hospitals for example. There are older analog paging systems that can be adapted to VoIP and Cloud based phone systems and there is newer PoE sip-based equipment that is just another device on the network. And then, there are VoIP phones that are be grouped together to into "paging groups" where you can treat them almost like like overheard paging speakers.
Multi-Cast technology has been around for a long time. The challenge in a cloud based world is that multi-cast is not designed to work well with NAT and transit the public internet (unless you plan to have VPN's everywhere which isn't ideal).
Multi-Cast is meant to be more LAN-based but even then VLAN's can cause a bit of a frustration especially if you don't have your traffic setup to pass between VLAN's which will surely be a problem in a multi-cast world.
SIP Paging on the other hand can transit the public internet and NAT however just like regular VoIP calls can be problematic if you have dozens or hundreds of phones being paged at once as every single device would be a seperate "call". Imagine if you were to page 100 devices at once remotely? That wouldn't bode well and in many cases may even be interpreted as a Flood Attack by many routers and firewalls. For small groups of phones & device it can do quite well!
There are many great VoIP appliances or Gizmo's out there. Here is one that cuts to the heart of what we are talking about. CyberData manufacturers a handy little device that can connect to your Cloud VoIP system as a standard extension but sit on the inside of the LAN as a Multi-Cast "man in the middle" allowing you to get the best of both worlds. Back to that example of a paging group with 100 VoIP phones, in this case it would be a single call from the Cloud VoIP system to this appliance inside the LAN and then this would trigger that page to all of those devices making things a lot more palatable.
A second cool feature is that this device can be used as a "Bell Ringer" which when called the appliance plays a bell audio that can be used as a night ringer when configured in a night ring group.
Good news is that this device is very affordable and for our North American Partners this device is now available in the bvoip partner store.