Well, I can't really help with the voice parts, but a while ago, I started a card-based unlocking project. Unfortunantly I never documented it my webpage, but I still have the programming and components on me. Basically, it used an ISO standard "track 2" card reader to could use most any card type as a "key," and this included domestic credit cards, driver's licenses and many others. The card reader itself had a 7-pin TTL interface that would make linking it to a PIC or AVR a breeze. Incidentally, Howstuffworks.com has a very detailed page on magstripe formats.
The unlocking system was a bulky solenoid-driven "deadbolt" that could unlock and lock a door using two solenoid types.
Anyway, if you're still interested, I'll look up the part numbers for this card reader and send you the card-reading assembly program.
Okay, here's that information I promised. The part was a Panasonic Magcard Reader model: ZU-M2121S that I purchased for about $4-$5. The attachment here is an AVR assembly program that was meant to be used with an LCD but it is heavily-commented and also organized by function. The reader pinout and card format is also featured in the program's title block.