How to get my dad to calm down?

I was on a Skype call (NOT video call) with a friend I met online 2 years ago. My dad walked in and heard my friend talking and demanded to know who I was talking to. I told him my friend’s name and my friend said hi. Then my dad asked if my friend lived in town or if I met him online. So I told him online. Now, my dad’s all mad at me. He’s telling me I shouldn’t talk to people I know online and stuff like that. I’m almost 18 and I know how to handle myself, I’m not stupid. How do I get my dad to realize that? I completely trust this friend. I have plenty of reasons to. But my dad doesn’t trust anyone. Not even people he meets in real life.

I wasn’t talking to my friend over the phone, it was over the internet, and my friend couldn’t SEE me. I don’t think this should be as big of a deal as my dad is making it out to be. I’ll be 18 in July, I think I’m old enough to make my own choices. Any suggestions?

Also, when I was 12 I had a friend I met online that I talked to EVERYDAY on the computer. He didn’t have a problem with that. So why all of a sudden does he now? I didn’t meet this friend in a chat room. I don’t go into chat rooms. And I have MANY reasons to believe that he is who he says he is. But my dad doesn’t trust my judgment.