It might help to broaden the question to: how can mobile devices provide meaningful information to businesses? With this, you've expanded the realm of use from

It might help to broaden the question to: how can mobile devices provide meaningful information to businesses? With this, you've expanded the realm of use from just quantifying ad efficacy to all activities a mobile device user might pursue. Perhaps there is a way to incorporate mobile internet use, cell phone use and physical location into a meaningful picture for the business, to help understand not only how many are responding to ads, but who they are - other interests/buying habits, other stores frequented, events surrounding decision to enter store/make purchase. Rather than a device owned by H&M, why not a service provided to all retail establishments?