I am a tech for a "reseller" or CLEC... there are good and bad to switching from the "main" phone carrier in your area to a reseller
normallay lower rates
usuallay faster / better customer service when calling in for billing issues
outside lines are only leased from the "main" phone provider in your area, and resold to you, so it is another link in the chain...
some companies do not have there own inside technicians (be sure the company you are switching to has inside techs, if you do not know how to troubleshoot and repair your phone lines)
may or may not offer wire maintanace...
if there is a trouble on your line, the "main" company which owns the lines outside is responsible for the outside wire repairs, you, or your local reseller is responsible for inside troubles.... while most troubles can be diagnosed with a line test, sometimes the test is inaccurate, and you have to wait for 2 techs to come out before the issue is resolved..
I say, if the company HAS an inside wire tech (or you or someone you know can maintain the inside wiring) and can offer you wire maintanace, then it should be worth it to switch...
if you have a high speed internet connection (cable modem, or DSL) you could save even more by getting VoIP from either your cable company, vonage, or some other internet telephone provider..