My boyfriend and I have been together for 6 months. Before that, we were very good friends and used to talk on the phone and flirt every night for hours. That is how i fell in love with him. After we started going out, I came to know that he talks to a lot of girls on the phone. He talks to them like 3 - 4 times in a week. He swears they are just friends and to be honest I know the girls he is talking to. But I fell in love with him by talking to him on the phone. Whats the guarantee that the other girls wont?

I told him how I feel, but he said that I should not be so insecure and jealous. Am i really being jealous and insecure or do I have a valid reason to ask him to talk less with other women on the phone?