Looking for cheap LD service

I need a cheap longdistance solution for calls within the US. The calling location is deep inside a building at Pomona College and cell coverage sucks.

Option A is prepaid cards. Genuine ATT cards are availabe on ebay for about 3.4 cents per minute. Or you can go even cheaper if you go to a site like CallingCardPlus — rates down to .5 cents per minute. I am sure quality on some of these cheap plans is iffy.

The location does have 10mbit ethernet and so VOIP is an option — I wonder what will happen when every student starts using VOIP, I bet the campus net is not engineered for that case. Free World Dialup – by pulver.com is a way to start, seems pretty geeky tho, you have to be a NAT expert — OK for me but not sure this will work for the caller. I wonder if Vonage is any easier to use. I definitely want an option that uses a SIP phone or a regular phone, I don’t want to use a PC mic and headphones.