This is getting fast and furious, but not everything I'm reading is true:
ISP's should consider using a DS1 or better to deliver dialtone for their modem banks. It makes alot of sense for the ISP and the phone company.
True, but...
Delivering dialtone over a T1 is certainly more cost effective than paying a %400 increase for Centrex lines.
...this is orthogonal to Centrex. You can deliver Centrex over T1 or copper. You can deliver 1ML's over T1 or copper. Centrex is a tariff change and an options change inside the telco switch -- but it's the same switch in most cases.
What does that have to do with anything? The T1 still drops into a phone switch and uses up channels.
True. But...
T1's are designed to stay up all the time, and centrex lines aren't. It doesn't really solve the capacity problem, but when Bell sells a T1 they sell it with the full knowledge that the line will be using all channels all the time (unless its a frac T). [...]
Nope, nope, nope. Telco expects the number of channels in use on a "digital service entrance" (T1 with DS0a channels) be precisely equal to the number of channels in use on 24 copper pairs. What the DSE saves is copper pairs, and cable weight in both the telco CO and the customer premise. DSE is also easier to diagnose problems with since the switch can tickle your CSU and run BERT without any physical human intervention. Some PUC's allow telcos to charge less for DSE, others (here in California for example) force telco to charge for the "bearer" circuit and also charge normal tariffs on the DS0a channels (1ML, Centrex, whatever.)
I can see Bell charging more for a Centrex line, but I can't see Bell charging more for a T1 or T3 _just_ because an ISP is using it.
The PUC-driven rate structures all take account of the cost of provision. Unlimited local calling (the life blood of the Internet right now) is priced at a low fixed rate because the PUC knows that most of those circuits will be on hook most of the time, and the ones that are off hook will usually have digitally aggregatable and compressable voice traffic on them most of the time, and the calls that have noncompressable FAX or modem traffic are assumed to be short and comparatively infrequent. None of this is true of an ISP customer, who tends to leave their link up for many hours at a time, generating noncompressable audio signals most of the time they're online. The telcos are within their rights to ask the PUC for a different rate, and the means to detect/enforce that rate, since the alternative is that they raise the unlimited local calling rates for all customers (even those not using modems for many hours at a time.) This wasn't an issue when only one person in 10,000 was an Internet user.