Mobot has a neat product. As user, you take photo of a print ad or poster, email it to a mobot-enabled advertiser (for example, Elle Girl firstname.lastname@example.org). You then get information sent to you from the advertiser.
The upside is that it uses mobiles (which everyone carries), and it's cool to use (if you have a camera phone, you're looking for a way to use it). Mobot has enabled mags like Elle Girl and Jane - and the readers (teen girls) are a particularly good target for a camera phone interaction service.
The downside is that as the user you have to register with the advertiser's mobot site, and you've shared your email / phone number with the advertiser.