Centrl, the newest multi-OS app offered by Apple, is yet another in the rapidly growing number of mobile social networking applications that has the potential to boost location-based advertising revenue...

Using Centrl, retailers can send coupons to users in their vicinity, and users can share coupons with friends.

However, Centrl enters the market at a difficult time for online advertisers. There has been no great surge in mobile ad spending, and most app makers do not anticipate much growth in mobile advertising until late in 2010.

According to Jeff Chester, executive director of the Centre for Digital Democracy in the US, social networking will dominate smartphone use for some time into the future. He adds: "We could very likely elect our next president based on who is targeting us on our mobile phones."

Yet the ad industry has been slow to exploit the opportunities that social networking offers.

Apple raised some eyebrows by initially announcing Centrl with a price tag of US$999.99. Now, though, the app is available as a free download through the iTunes store. It runs on iPhone, Android and Blackberry, with Windows Mobile and Symbian compatibility in the pipeline.

Centrl users can see the location of Facebook friends and send them instant messages. It can mark a map location to tell friends about a good restaurant, store or nightclub.

Apple claims that Centrl has the best privacy policy of any current location-based social network. You can become 'invisible' and Centrl doesn't sell or store your location history. Every new location update overwrites the previous one, and all location data is erased if there is no location update after one week.