Let me preface this by saying it really is accidental. I have had this "phenomenon" my whole life.
I know I am not alone in this. I'm from Maine and have a "Maine accent". Not the downeast Maine accent, nor the northern accent. But, it is definitely there although I am losing it since being down in this area of Florida.
My thievery is of others voice tones and their accents. For instance, my cashier at the farmers market has a very strong New Zealand accent. While speaking to him, suddenly my voice thinks it too is from New Zealand. I sound quite silly, but for some reason I cannot control it. That man from Texas talking to me at the health food store? I suddently have a Texan drawl...only we all know it must sound awful fake. The New Yorker bagging my groceries at Publix? You can guess how I start talking.
I also tend to pick up on the tones people are speaking to me with. I will get very soft with a soft spoken woman, or very brash with a loud man. Deep voice? Me too! I'm not sure why this happens, but I can remember instances from various periods in my life. Maybe it's some weird insecurity in me, trying to fit in. I really don't know.
Luckily, around my husband and son I talk in what appears to be my own voice. I have the ever so slight southern accent developing, and I don't mind. So, if you are talking to me and notice I'm beginning to sound just like you.....I apologize in advance.