D.P.
hi michelle
i had the same exact problem w/ my older house in the casa linda area.
IT IS the phone line.
don't hire an electrician yet.
make at&t come back out and really inspect those lines outside.
here's what happened at my house.........
they came out 3 times, always telling me there was nothing wrong w/ the lines outside. the last time, i had them come into the house and check the outlet before they left.
the guy hooked something up to the phone line inside the house and that's when he realized........oh, this is an outside line problem, even though he had just told me 5 minutes before that the line outside was fine!
he climbed back up and discovered that way in the back of the box, where he had not looked, yes, in fact those telephone lines were soaked from the rain.
after he fixed it i've never had another problem.
other than w/ at&t, so i switched phone service..........
good luck but please try to make them check the lines again.