Telo Systems is a manufacturer of PoC devices. These devices communicate over cellular (3G, 4G and soon 5G) and/ or WIFI.
Telo has a lot of different options from a simple hand held to a all round robust device.
Explore the Telo Hardware:
Telo Systems also offers a Push To Talk Platform called TeloPTT what can be used to communicate with each other.
The main benefit of using 4GPTT is that you can communicate worldwide with one press on a button without investing in your own Push To Talk infrastructure.