"Twinkle" is a Twitter client for the iPhone that also shows you people who are using the service near you, thanks to the GPS feature of the device. On second thought, Twinkle isn't just a Twitter client -- it's a competitor.

Since Twinkle is a location-based microblogging brand very close to Twitter, the smart folks over at Twinkle realized that to create a user base, all they need to do is allow you to create an account with your (already validated to be unique) Twitter username and password.

Half of the Twinkle service is providing you with an iPhone-interfaced way to stay in touch with your Twitter friends, while the other half only feels like Twitter. It's really the Twinkle network, showing you Twinkle members that are within a certain radius of you. Pretty sneaky.

What makes this interesting for brands is the immediacy with which I can find people with common interests close to me. They're Tweeters with iPhones, and they're right here!