I follow the 'Hello, may I help you?' model, and often get distracted for middle brother, who is twelve. We both think that our voices sound nothing alike, but...

I mean, there's the whole deal where his voice is much higher than mine.

But oh, I just realised that I pitch my voice rather high over the phone, because I used to get mistaken for my mother (which is really a 'WTF?!' type thing). Elementary, my dear Watson.