Israeli company MobiApp announced that it received a small funding round from Maayan Ventures, an Israeli government-funded VC. The company has a social networking mobile app/client called Mingler, currently operating only is Tel Aviv, Israel. Here's how the funder describes Mingler:

Mingler enables creating close range social networks which interface the WEB.

When a user enters the social event he will receive a message in his mobile which will ask him if he wishes to connect to the local network, after he confirms he will join the Mingler network.

The user doesn't need to have any prior application installed; he will get the application on the spot by the air with no cost (based on Bluetooth).

The Mingler lets the user fill his local profile and in the future this profile will be available on his web social network. The users can send (and receive) personal messages/Instant messaging (like SMS but without charge) to his network friends and of course search, filter etc'. All the users are in the same location which is defined by approx. 100m radius (can be extended with aggregation) are connected to the local network. This creates a free local network.

The Mingler website will provide lots of web/location services to Mingler members for example: getting the location of your friend and sending them free messages from the web, it'll give the option to see who is in specific event and more.
Moreover Mingler will allow the users to interface with their WEB social networks(FaceBook, mySpace, linkedIn…).

The application and the services are free for the users but it is based on ads, this gives advertisers the option to advertise to specific market focused by: gender, location, age, company segment, position in organization, etc.

At the moment there isn't ad inventory "granular" enough to fulfill the promise of these temporary, very local networks envisioned by MobiApp. That will come as more LBS ads are assembled "on the fly" dynamically. There are a few use cases one can think of for Mingler: B2B (conferences), colleges or other institutional settings and dating.

The fact that this rides on top of existing social networks is a significant factor. Stand-alone mobile social networks will find it almost impossible to compete with established online players such as Facebook and Twitter. There may be one or two exceptions that succeed.

Services like Loopt and Google Latitude are competing friend-finder/dating platforms.