Jeff Allen vs. the time suck vampire

Fourteen-year-old Jeff Allen, cancer survivor, is not sure which problem facing him is more troubling, dealing with a prosthetic leg or replacing the cell phones that were destroyed by the monsters his parents do not believe in; but when he offers to work at Mr Ogilvie's store (for a phone) he encounters the Nosferatu cell phones with a killer app--literally, because it causes people who use it to become raging lunatics with a vampiric thirst for blood.