Modem Incompatibilities

For several months now I have had real problems while using internal modems with Intel chipsets. They won't connect, make strange constant noises, and sometimes will knock out the other phone lines in the store (until the telephone line is yanked out of the modem). We have to use Lucent chipset modems exclusively. They work fine.
We used to be able to use Intel modems, but something changed a while ago. I spoke with a computer parts distributor who lives about 40 miles from here and he said that he encountered the same problem in a large rural area there.
We are all served by Verizon. Maybe that's the common denominator.