Nowadays QR codes have more or less taken over from other 1D and 2D barcode technologies for mobile marketing, even though also UPC/EAN codes are used.
Obviously the latter are not nearly as flexible, as they are used for specifically identifying products (you buy code ranges) , but I can think of campaigns where you would enter or scan UPC/EAN codes from products for rebates, sweepstakes etc.
Even so, QR Codes is where things happen, for the most part, and this article highlights a few pros, cons and hurdles with using QR codes for marketing.
Reality Check- Fee vs. free – navigating mobile 2D barcodes – RCR Wireless News
MM3 (one of my co-owned companies; the site is in Swedish) offers a service for handling routing and tracking of QR codes specifically for mobile marketing. Let me know if you are interested in discussing this further.