PTT Radio Communication via LTE/4G & 3G. Using an existing LTE (4G) and 3G network, the IP503H is able to provide a network with wide area coverage capabilities. The IP503H does not require its own repeaters or IP network which reduces the cost of building and maintaining a wide area radio network. Full-Duplex Communication: The IP503H enables use of full-duplex communication which provides smooth telephone style conversations. The IP503H users can talk and receive at the same time.