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. Delivering dialtone over a T1 is certainly more cost effective than paying a %400 increase for Centrex lines.
What does that have to do with anything? The T1 still drops into a phone switch and uses up channels.
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). From what I read, the major concern was problems in planning for switch capacity. Bell really doesn't have a way of knowing that the Centrex lines they just sold to a company (that just happens to be an ISP) are going to be up all the time. This would not be the case if the information collected from the Bell sales rep filters all the way to the people doing the planning (which I doubt it does). 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. Scott