Still on at&t GSM. What if I lose SIM card???

I am still on my old AT&T contract and would like to stay on that plan after my contract expires in a month. I spoke with Cingular and they said I can stay on with the same terms month to month as the AT&T contract but if I lose my SIM card by some bad chance, my plan will automatically be cancelled and if I want to stay with Cingular I will have to get a new plan at a considerable $$$ increase for the same minutes as the old AT&T plan.
Is there something Cingular is not telling me about this or is this totally true?
Can I get a SIM card to use as a backup in case I lose the one I have?
Appreciate any advice on this.

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I doubt it. Cingular is trying to make it as difficult as possible for customers to stay on the old plans.

And besides, it's really hard to find an ATT SIM card. None of the Cingular stores that I know of still carry the Blue cards...already hard enough to find non 3g cards as it is.