I've had no problems with our current telco, though it might have more to do with the services we do (don't) use than anything else.
I have been with TDS for five of more years now. We review every bill and have not found a single unauthorized charge. Prior to that, we were with Qwest for around 10 years. During that time, I remember finding one or two unauthorized charges, but they were quickly removed when I called in.
With our current telco, TDS, our bill does not vary from month to month. We have an unlimited local calling pack and our DSL service. We do not have a long distance carrier. No long distance calls may be made directly from our number. We requested the block when we established our service because we either used calling cards for long distance (at a little over one cent per minute), or our cell phones (no distinction between local/long distance calls). Because of that, our bill remains the same every month. If the bill ever is different, we can see it immediately. So, the two times we've used 4-1-1 service from the house were easy to spot, as was the change in the billing amount when we upgraded our DSL service (a price drop!).
I'm guessing that it is much easier to "cram" charges on accounts that have long distance services and limited call packages, since consumers expect that their monthly bills will vary. So long as the charges don't push the bill beyond where it usually falls, most people likely just pay up and wait for the next one.