TechCrunch offers a list of new start-ups operating in the space they call “the holy grail of mobile social networking”: “physical presence detection and information exchange with other users.”

Aka-Aki (Germany): “create a profile and download the java app to your phone. You can also create and join groups that say things about your life, job, etc. When you are near other people who are members, data about you is transmitted to them via bluetooth, and vice versa. Users have control over data flow with privacy settings.”

Imity (Denmark): “it detects other members via bluetooth and send basic profile information to your phone. It also keeps track of people on its website, so you can check that out periodically from your normal computer. It’s bridges mobile and traditional social networks, which may help it gain critical mass.”

MeetMoi (USA): “it uses text messaging to help connect people. It’s dating focused – text your location to the service and it notifies other users in your area that you are there. If they are interested, they can contact you.”

MobiLuck (France): it “is another bluetooth solution similar to Aka-Aki and Imity. Download the software to your phone and it vibrates when other users are nearby. You can then chat with them, send photos, etc.”

BrightKite (USA): “serves location based notifications (”place streaming”) over email, instant messaging of text messages. The idea is to stream content about a place, from a place. Friends are alerted when you are nearby. You receive offers from local businesses. Etc. Targeted towards conferences, bars, parties and public places. It is also a platform for third party applications.”

What it means: Talking about critical success factors, TechCrunch mentions that “what’s harder is just plain getting a critical mass of users.” I would answer that’s only one side of the equation. The other one is monetization and I believe local advertising plays a key role there. If you operate a local play, you should be thinking hard about your mobile strategy today. My gut feeling is that we’re 18-24 months from real breakthroughs in local mobile advertising but, when that happens, it might become a very important source of revenues. How big? The Kelsey Group just released a report on US mobile search advertising revenues and they forecast that it will reach $1.4B in 2012.