First a quote:
Mobile phones are establishing themselves as an important way for retailers to connect with consumers and entice them into purchases, according to a pair of studies released in May 2012. Data from an Ipsos survey finds that within the US, roughly one-quarter of consumers have opened a retail email on their mobile phone, with that proportion rising to 37% among consumers aged under 35, 32% among business owners, and 31% among those with high educational levels of attainment. Beyond opening emails, mobile owners are also interested in receiving vouchers: according to an eDigitalResearch survey, more than half of smartphone owners would be fairly or very interested in receiving vouchers sent to their devices.
And an interesting chart: