I was told when this happened with ATT a few weeks ago that the account owners phone was fucked and all the sub accounts were good plus business accounts were unexpected.
I lost coverage for 5 hours on my personal ATT phone but I was able to use my work ATT phone to call my wife.
My brother was having the same issue. He could call people just fine while his girlfriend couldn't. He discovered that he can't call anyone that has an iPhone and they can't call anyone else.