THE annual SXSW Interactive festival in Austin, Texas, is a blur of panels and parties, as social-media entrepreneurs and investors scramble to corral the early adopters who can push their products into the mainstream. Twitter has not looked back since its SXSW debut, four years ago, when it proved an instant hit among festival-goers.

This year GroupMe, a “group messaging” service, said it had given away 2,500 grilled-cheese sandwiches over the five days of the festival. GroupMe defeated several lookalikes—including Beluga, which Facebook has just bought—to win the festival's Breakout Digital Trend award. It also handled more than 2m messages a day relating to SXSW—a huge boost to its traffic that must work out at thousands of new users per sandwich, a pretty good return on investment.

Group messaging is simple. One texter sets up the group, online or with a smartphone, and invites others. The group gets its own phone number, and a text sent to that number goes to everyone in the group. Even people with dumbphones can take part. That makes it work for those stragglers who still do not have e-mail on their mobiles (although some of GroupMe's competitors work only on iPhones and Android phones).

This is a handy variant of social networking. Sites such as Facebook and Twitter are essentially public (though users can restrict who sees their messages); indeed, they involve an element of performance. Group messaging represents a step back from broadcasting. It preserves some measure of intimacy and exclusivity. Beluga, for example, asks users to sort their contacts into “pods”, each serving as a distribution list.

It all sounds useful, but how is it going to make money? GroupMe, which raised $10.6m in January, is mulling advertisements tailored to groups. But users may not welcome a spambot suddenly weighing in on their dinner plans. Etiquette questions will also arise among friends. Group texting is logical when membership has already been delineated—for the team-mates on a project, for example. Among friends, there will surely be tiffs over who is in, and out, of which group. Despite such worries, group messaging looks destined to be old hat by the time next year's SXSW comes around.