TEL AVIV (Reuters) - An Israeli scientist said on Wednesday his team had found a way to break into mobile phone calls made on the popular GSM network, allowing eavesdroppers to listen in on calls and even take on a caller's identity. The GSM Association, representing vendors who sell the world's largest mobile system, which is used by more than 860 million consumers in 197 countries, confirmed the security hole but said it would be expensive and complicated to exploit.