Has anyone read the Friends and Enemies series by David Field? I just finished reading the 2nd book in the series (Beings in a Dream). The books are about a 15 year old named Tommy who is vacationing in France with his family when he goes back in time 400 years (and takes his cell with him). He meets Eloise and falls in love and the two of them have adventure after adventure as they try to escape/defeat the evil Drogo (he is a great antagonist). In the 2nd book, the characters return to the present time, which lead to some seriously funny culture shock for Eloise!. The books are sort of a cross between fantasy, sci-fi, adventure, and comedy. I enjoyed them, but they seem to be a bit obscure. I found them on Amazon. Haven't found them anywhere else yet.