3G and LTE (4G) mobile phone network is in place throughout the MTR system of stations and tunnels allowing passengers to stay connected underground. Currently, full 3G network coverage in all stations and tunnels (except underground section on East Rail line and West Rail line) for the MTR system has been provided by 3 Hong Kong, SmarTone and PCCW. Passengers are able to use high-speed internet on their mobile phones regardless whether the train is above ground or under ground. The MTR has already extended the Wi-Fi service to all of the Airport Express trains and the expansion of the service to other MTR routes is still under consideration by MTR. All 93 stations on the MTR offer free Wi-Fi service with a limit of 15 minutes per session and a maximum of five sessions per day.