I'm a BC grad (from the Philosophy MA). The department does notify its initial PhD acceptances via phone, and they've already done so this year. The line about official university policy is just that--a policy of the university, not the department, and a way to save people in the admissions office the trouble of talking with applicants about the status of their applications.
That said, there's always the possibility of a wait-list acceptance. But that, too, would likely happen by phone.
Letters from BC are generally either offers of admission to the MA program, or outright rejections. Good luck!