Whatshisface — Gordon Korman

When 12-year-old Cooper Vega moves for the third time in five years, he receives a state-of-the-art smartphone to help him stay in touch with old friends. He's had phones before, but this one is buggy and unpredictable. When a boy named Roderick Northrop communicates with him through the phone, Cooper realizes that his phone isn't buggy at all; the thing is haunted!