Was that Lie Necessary?

I was then in Delhi.  My friend happened to come there from Chennai for a week.  When he called me on phone, I asked him whether he had brought his mobile phone so that I could be in touch with him when he was in Delhi.  He said he hadn't brought it but told me that he would stay in touch with me.

Two days later, he joined me for lunch. At that time I saw him answer a call in a mobile phone. I asked him whether he had borrowed his friend's mobile in Delhi for sometime.  He said it was his own Chennai mobile. Even as I wondered why he told me earlier that he hadn't brought his mobile, he told me that he didn't let anyone know that he had brought it as they would call him on that number and he would have to pay roaming charges if he took the call.

I felt a little disturbed by his remarks. He could have told me the truth and asked me not to call him on that number unless there was something very important. Why should he unnecessarily tell a lie to me? The whole thing is very trivial but still