I realize this is probably something one learns in Telco 101, which I haven't taken, but if CNID == Caller ID, wouldn't ANI be *more* useful?

It depends on what you want. A real call trace is more involved. But if all you are interested in is the billing information, then ANI usually works. If all you are interested in is the directory number then CLID works. In general, it is bad news for ISP geeks to play telephone guru, and bad news for telephone geeks to play ISP guru.

Or does CNID report the number regardless of Caller-ID blocking on PRI lines/etc?

No. Assuming the telco programs the switch correctly, blocked CLID won't be passed on subscriber lines. Mistakes happen, but don't count on it.

(I'm assuming that CNID == standard Caller-ID as it appears on POTS, and that ANI == the special service that 800-lines get that *always* reports the number, regardless of blocking..if I'm wrong, I'll accept the LART.)

The alternative is to become a CLEC, and buy something like a FGB circuit with ANI or full-fledge SS7 trunks with per-minute usage fees, aka settlements. If you only want to pay standard POTS rates for your dialup lines, you only get standard POTS service. I think the telco's blew it when they tried to impose per minute fees on ISPs. Rather than thinking up nifty new services ISPs might want on the lines, and create a demand for improved lines, the telcos tried ramming through tariff changes for more money for the same service and ended up losing even more. The current dialup/packet-switched interface is such a kludge anyway. We've got to work on getting real packet-switched data service to the home for a number of reasons, not the least to get rid of this interference layer between the circuit switched identifier and the packet switched identifier. -- Sean Donelan, Data Research Associates, Inc, St. Louis, MO Affiliation given for identification not representation