SEATTLE—A Pakistan resident has been sentenced to 12 years in prison for a conspiracy to “unlock” phones from AT&T’s network, a scheme the company says cost it more than $200 million. Muhammad Fahd, 35, of Karachi, recruited an employee of an AT&T call center in Bothell, Washington, via Facebook in 2012, and began bribing that employee and his coworkers to use their credentials to unlock phones. That allowed the phones to be removed from AT&T’s network, even if customers had not finished paying for the expensive devices or their service contracts had not expired. The customers could then buy cheaper service for their phones. Fahd later had workers install malware on the company’s network, allowing him to unlock the phones from Pakistan. He persisted even after the company detected the initial scheme and fired two of the workers involved, prosecutors said. Fahd sold the illegal phone-unlocking service through online retailers, …