Germany engineering firm Siemens says its working with Airbus to develop technology for plane passengers to use their ordinary mobile-phones during flights. Airbus will build the systems into its existing electronics, market them to airlines and maintain them. The lightweight on-board base stations linked to satellites connected to the GSM mobile network will be supplied by Siemens. The technology will ensure calls do not interfere with aircraft systems or mobile networks on the ground. Consultants Booz Allen Hamilton believe the European market will be worth up to two billion euros annually within the next four years, with as many as one hundred million users.Calls are expected to cost around one euro a minute initially, but falling to around half that price within three to five years. Still being worked out is how revenues would be divided between mobile-phone operators, airlines, satellite operators and aircraft manufacturers. The technology is also suitable for aircraft made by Airbus rival Boeing. The US company already has technology on its planes for on-board broadband internet access. It also expects to start selling cell phone services to airline passengers by next year.