No, the old cingular sim cards use a 2G technology, or at best 2.5G, they also have less memory than the newer sim cards. you can use the old phone, and sign up for a pay as you go plan, that just deducts the money from your account without having to sign a contract, you will have the same service as a person with a contract call plan, but no contract. and pay out of pocket for the sim card. if the phone is very old (analog) then you can't use it at all, since the system is all digital

You can buy an unlocked phone or any Cingular branded phone as well as many AT&T branded phones your Sim card will still work in those phones the issue is that AT&T needs to provide you with a newer "3G" compatible Sim card in order to perform an upgrade in their current billing system as AT&T has discontinued support for non 3G Sim cards going forward. The phone would still work if you simply purchased it at retail but you might have to contact AT&Ts Regional Subsidy Unlock Team to unlock it if your Cingular Sim is too old. If your Sim card has a little flame logo and "3G" on it or says 64K on the underside it should work in any current AT&T phone. If it says 32K you probably need to bite the bullet and get the upgrade if its 64K it can be upgraded with any current AT&T phone without 3G support such as the Blackberry 8310 without getting a new sim however.