Frankly, it all sounds confusing, and I see this as a major reason NOT to go with AC ...
Even if the dual systems work eventually, the switching hassles, and thus the switching costs, are high, and dealing with two customer-support services has got to increase the headaches by more than just 100%.
Very frustrating. The outsourcing of billing services seems like a good alternative on the surface, but as some have noted, decreased collections seem a certainty. I'd prefer to keep billing as close as possible our own business.
