Changing height of camera based on device aspect ratio. How?

So I want to make a game where the width is important, otherwise the game would be easier of certain devices etc. So I wondered if anyone knows a way of making the width of the camera set, and allowing the height to change based on the aspect ratio of the device, but in perspective. I can find stuff to do with orthographic cameras, but nothing on perspective. Oh, and I use unityScript if needed. Thanx :)