I looked at the AT&T site that XBanker linked. In the user agreement it specifically states that "minutes don't expire", which is great. But check this out:

- "...A surcharge not to exceed 10 minutes applies to U.S. pay phone calls, some of which compensates pay phone providers."

- "...For calls that begin and end within the same state, minutes are deducted at the following rates per minute of talk time: 1 minute: DC, IL, IN, MA, RI, USVI; 3 minutes: AL, AR, CA, CT, DE, GA, HI, KS, KY, LA, MD, ME, MI, MS, NE, NJ, NM, NV, NY, OH, OR, PR, SC, TN, UT, WI, WV; 5 minutes: AK, AZ, CO, FL, IA, ID, MN, MT, NC, NH, OK, PA, TX, VA, VT, WA, WY; and 8 minutes: MO, ND, SD."

WOW! One minute of intrastate actual talk time is billed as 3 to 8 minutes off your card in most states. So in my state, a "300 minute" card is really just a 100 minute card. Amazing.

Thanks for all the replies you guys.