According to slickdeals Google Voice and iPrint are or were giving away 50000 free sets of 25 Google Voice Business cards in the continental USA. I did not find the Google Voice link to the offer.
http://forums.slickdeals.net/showthread.php?sduid=0&t=1467659

three card styles:
http://a2.slickdeals.net/attachment.php?attachmentid=237319&d=1248406126

Techcrunch has the link (available to Google Voice users only):

https://www.google.com/voice/promo/iprint

Via: http://www.techcrunch.com/2009/07/23/google-voice-gives-out-free-business-cards-makes-switching-numbers-slightly-less-incredibly-irritating/

promo's over, but check this link out that was posted on in your slickdeals link:
http://printmvp.com/google-voice-promo-business-cards

Promo is not over. i just did mine.

Yeah, guess it's not over; just saw my link appeared today under my balance.

I actually placed an order from the prior link I posted and got my cards on Friday. They actually exceeded my expectations and I like how my company logo is printed on the other side. Guess I'll order a free set too...why not, lol.