When I was 17, pretty much everyone mistook me for my father when I answered the phone, even his parents (my grand parents) and his brother (my uncle). Usually I let the conversation go on a few minutes before I said "wait, let me get dad". I sounded exactly like him, though my mother always knew the difference.
My younger son sounds like my husband on the phone also. It takes me a second to figure it out when my husband is out of town for work. (That son lives three hours away.) On the house phone caller ID is the same for both, and their cell phone numbers are very similar. I can figure it out, but others have gotten them mistaken for longer.