Tokyo based Wire & Wireless has announced (Japanese) that it will be providing subscription wireless broadband services for the airport limousine bus services at Narita and Haneda. The company hasn't yet indicated their fee schedule but the buses are being fitted out from the beginning of this month and the service will be available in all from the 1st June. It will be widely advertised in several languages at the airport arrival gates. Wire & Wireless say they are also working on providing broadband for taxis while the JR companies unveiled their shinkansen broadband infrastructure last month.
