[SirMonkey]

If we are talking about the radio spectrum: Not much - other than the threat of the regulators showing up at your doorsteps after they found you with a van. If you are talking about the backbone so to say, it's not such a big Issue. The original packet-forwarder sends "json" over UDP. If you are using a packet-forwarder by one of the network operators, some of them are using MQTT (IP/TCP) as the transport.

Some gateways let you filter by network_id, this will not stop someone from pulliting/disrupting the radio spectrum, but it will stop your gateway from relaying those packets to your network-server.