Though smartphone shipments are rising and expected to surpass shipments of feature phones in 2011, according to Morgan Stanley, feature phones are still the devices in the hands of most mobile users. An April 2010 ExactTarget study found 58% of all US internet users ages 15 and older had one, compared with 31% who had a smartphone.

That means a large swathe of mobile users cannot be reached by more sophisticated mobile marketing efforts like sponsored apps, in-app ads or campaigns on the mobile web. According to location-based advertising network 1020 Placecast, opt-in text alerts are the smart way to target a fuller mobile audience.

A May 2010 survey conducted for Placecast by Harris Interactive found that while most mobile users still have not signed up for any text alerts, there was a small rise in interest since a similar poll in 2009: 28% were at least somewhat interested in the alerts, up 2 percentage points, and 8% were extremely or very interested, up 3 percentage points. For under-35s, interest was significantly higher.

Those who wanted the alerts were most interested in coupons and promotions from grocery stores and restaurants. Respondents who had signed up for text alerts said it made them more likely to visit the company’s website (34%), visit the store (33%) and purchase the product being promoted, either in online (28%) or in the store (27%).

Many agreed that making those text alerts location-based, so that recipients would get the right offer at the right time, could make the channel more useful or interesting.

While awareness of location-based text alerts is still building, there is the potential to reach a broader audience than with check-in apps such as foursquare or Gowalla, which are designed with smartphone owners in mind. And despite negative attitudes of many mobile users toward SMS marketing, Placecast reports low opt-out rates among recipients.

“The brand faithful view these kinds of alerts as a service, not just marketing or an intrusion,” Placecast CEO Alistair Goodman told eMarketer.

The social networking audience in the US has reached critical mass. eMarketer estimates that 57.5% of all US Internet users, or 127 million people, will use a social network at least once a month in 2010. By 2014, nearly two-thirds of Internet users will be on board.

Marketers have been chasing this audience for several years, but the question remains: Do consumers notice, or care?

“Those who still think that social network users are too busy engaging with friends to notice marketers must change their viewpoint,” said Debra Aho Williamson, eMarketer senior analyst and author of the new report “Brand Interactions on Social Networks.” “Brand interactions are real, valuable and growing. “

According to a February 2010 survey by Chadwick Martin Bailey, a market research firm, 33% of Facebook users have become fans of brands on the network.

Another survey, by Edison Research, found that 16% of social network users had friended brands there. And half (51%) had done so on Twitter.

Coupons remain a leading driver of brand interactions in social networks. Learning about sales and new products is also a strong motivator for people to interact with companies in social media. Beyond the tangibles, such as coupons, consumers do gain positive feelings about a brand as a result of their interactions.

Still, social networks are not seen as primary research sources when consumers are looking to buy. Although people are very inclined to take advice from friends and family about products they are interested in, they are not nearly as likely to seek out their social network friends when they are researching online.

According to a study by PowerReviews and the e-tailing group, only 3% of online buyers said they sought recommendations from social network friends first, compared with 57% who started with search engines.

“More than half of all Internet users now use social networks, and the percentage of social network users who talk about companies, either in organic conversations or on branded company pages, is growing,” said Ms. Williamson. “Consumers do pay attention and they do value positive interactions with companies.

“But while people trust their friends for advice and use social networks as part of their research process, social networks are long way from replacing search, if they ever will, as a source of information leading to a purchase.”