Is there a difference in advertising response rates for the various
toll-free exchanges?

I want information about toll-free numbers starting with 800 vs. 866
vs. 877 vs. 888.  Is one exchange superior to another?  Do 866, 877
and 888 numbers receive as many incoming calls, percentage wise, as
traditional 800 toll-free numbers?

I want statistics on whether or not consumers realize that the 866,
877 and 888 exchanges are toll-free.