The moment I got Foursquare? About midday on Saturday when I checked in at a department store in Cologne. I've been using the service for a month or so, checking in, looking at reviews, adding places. But I hadn't quite worked out the real commercial possibilities of the software.

So why Cologne?

As soon as I checked in, up flashed a 'nearby offer' sign, which linked to a message from Vodafone. Here's how it worked. In the same street there's a Vodafone retail outlet, which was giving away netbooks and other prizes to its Mayors at midday and 3pm.

There's more to this than neat marketing on a slow January weekend. Remember cybersquatting? When you could register the name of a big business and negotiate, if you were savvy enough, a payout for your URL? Much the same is happening with Foursquare. Except now it's smart web and gadget users who are grabbing online real estate by becoming Mayors or simply visiting frequently and posting reviews.

The implications for pretty much any consumer facing business are enormous. Imagine Twitter, but with all that chatter about your company organised coherently around multiple locations and outlets. No need to invent tools like retweeting or hashtags, when the work is done for you already.

As far as I can tell, anyone can add a place, make it visible to other Foursquare users and start the conversation. Imagine trying to exercise any control over such fragmented ownership. At least a URL has one owner.

Which brings us back to Cologne and Vodafone, a company that's already started to engage with visitors and which understands the implications for its business. I doubt very much that it's the first to turn Foursquare to its advantage and it certainly won't be the last.

A final thought. For all the hype, Foursquare has just 100,000 users worldwide. If you want to go get some of that there online real estate, now's the time to get moving.