Lost Number by Ashley May

Sorato Hideki is a latchkey-kid, accustomed to being picked up and dropped off in whatever town his father's whims take him to. When he's sent to the sleepy town of Midorioka to live with a relative he's never met, he thinks little of the situation.

However, rumors crop up in Hideki's new school about mysterious "haunted payphones" all around Midorioka. What at first seem like abandoned relics the city is too cheap to have removed, soon show themselves to be much more...