Target has begun offering coupons to their customers via cell phones.  They are then redeemed by scanning a barcode at checkout.

According to the news release, Target is the first national retailer to offer scannable mobile coupons.

You can opt-in by going to www.target.com/mobile on your computer.  To opt-in using your cell phone, go to m.target.com or text COUPONS to 82738.  You'll then get a link to the mobile Web page.  The page will have multiple offers that can be accessed through a single barcode.  The offers do have an expiration date and can only be used once.

You will receive exclusive offers once a month via a text message.  Your first "coupon" will arrive within two weeks after you sign up.