I bought myself a long-distance phone card, called Marca Ya, when I was in Veracruz. Ever since, the damn thing has given me nothing but problems. First, it refused to work at all. Then, when it did work, it seemed to charge more per minute than it was meant to. And now, it's expired itself about 2 months before it was meant to. I am officially a dissatisfied customer. If you get to Mexico, stay away from Marca Ya phone cards: they suck.
When I tried using my card today, and the voice at the other end told me "su tarjeta ha expirado", I called the toll-free customer service number. My call was important to them for about 15 minutes, then I finally got put on to a human, who even spoke good English. He was nice enough, if a bit hopeless. He told me that there'd been some mistake, and that my card should still be valid, and that they'd have it un-expired again within 2 days.
Well, they better have it done within 2 days, because I'm only in the country for another 3.