A common problem. Telephone providers, both local and long distance, have to spend time and money resolving such issues. Sometimes the dollar amounts are significant and the dispute makes the newspapers. It's tough to say who is at fault -- customer, base telephone provider, or long distance carrier, or combination.
We all have to pay for this through higher rates and aggravation.
I noticed some respondents said this was a reason they're switching to VOIP, but I it seems most VOIP are keeping one POTS line as a backup. I suspect getting VOIP to reach that "last mile" of service reliability to equal or exceed classic POTS will take some time in coming and be considerably expensive. (Can VOIP handle faxes transparently?) As an example, the 911 requirement was repeatedly extended; that was something the VOIP people should've had all set up and included from day one. In other words, down the road VOIP will cost much more than it does now.