My guess is that as a traveller we don't provide the local telecom companies recurring revenue like the local residents so they will charge us more for using their networks. Your service provide will charge you for roaming and in turn your service provider will be charged a fee for pigging backing on the host countries' network. There may also be taxes incurred through cross borders communication to the governments. Therefore layers on layers of fees in which we ultimately pay for. Win-win for those providing the service whereas we lose-lose!