Adam Greenfield, who coined the term moblogging to describe the combination of mobile telephones and weblogs, urges mobile service providers to encourage the practice.
(Thanks, Adam!)
At its simplest, what this means is that people carrying these devices everywhere they go can post their experiences, narratively and visually, on a shared message board. The technology need not be any more sophisticated than that driving the average Internet discussion board, but the experience of participation is tremendously enhanced. (I call it moblogging.)
Help your customers understand this. Offer them a gently branded space where they can share their stories, let a community accrete around it. Let users' allegiance develop to that community, which will be a lot realer and deeper than their entirely notional loyalty to a brand. I guarantee you it will be the stickiest thing since asphalt in August, because it will take a lot more than a competitor's superficially sexy phone to wean people away from real relationships they've built and nurtured. (Extra credit if you can somehow make the postings location-specific, and thus tie the digital back to the lived experience of the city.)
