Koizora (2007)

During her freshman year in high school, Mika Tahara (Yui Aragaki) loses her cellular phone, but later finds it in the school library with the help of an unknown caller. Throughout the summer, Mika and the mysterious caller continue to communicate, and agree to meet each other once school starts again. The caller turns out to be Hiro (Haruma Miura), a delinquent-like boy Mika is initially afraid of, who shows proof of his identity as the caller with a photo of the sky on his cellular phone.