If This is happing on all pots lines the posablity of it being a phone co. problem is nill.
Votage spikes is an excelent possability.
I think removing the apc for a week would be a good test. also changing the wall outlet is a good test but doing both at the same time won't tell you witch one is your culpert.
Recycling the switch can cure thees intermittin
problems. Because it refreshes the cpu.I would choose this as my first choise.