My friend in college, he is gay. When we first met him, he had, what would be deemed, a 'normal' toned voice. But, day by day, gradually, his voice gets more 'camp', higher pitched, more stereotypically gay.

If he wasn't so flamboyant in his vocal chords, then maybe he would be rejected in a gay environment? Maybe he feels that this is a pre-requirement, subconsciously adapting himself to such as to be accepted within a group.