Using a mobile phone will become significantly less expensive over the next few years, according to an expert. "We expect that speaking on a mobile phone will cost at least 20 percent less every year," Martin Gutberlet of Gartner research institute told DPA news service. German mobile phone operator e-plus recently began offering a discount mobile phone service with calls at 19 euro cents (23 US cents) per minute. Mobile phone companies already have seen their revenues drop by a quarter in the past four years due to cheaper rates, according to Gurberlet.