PostUp is a Twitter search and advertising company that used to be known as TweetUp. PostUp has acquired Echofon. Echofon is a company that develops Facebook and Twitter applications that is used by about 3 million people. PostUp was incubated at Idealab and started allowing registration for their real-time search engine last year. PostUp also recently acquired Twidroyd and popurls. [TechCrunch]

TweetUp, a service that focuses on advertising and searching Twitter, has made two acquisitions. TweetUp bought Twitter Android client Twidroid. TweetUp acquired news aggregator service popurls.

Incubator company idealab is launching a new startup company called Tweetup. The man behind Tweetup is Bill Gross. Gross is the original founder of GoTo.com. GoTo.com was renamed to Overture, a company that Yahoo! purchased. Yahoo! was able to leverage Overture patents by suing Google and settling for a settlement of 2.7 million shares.

Tweetup is a Twitter search engine that has an advertising platform. When you search for tweets using Tweetup, the search engine will use an algorithm to place important tweets at the top and contextual ads on the side.

If you integrate Tweetup into your own website, you can share 50-50 revenue with idealab. Tweetup already has an established partnership with Answers.com.

Investors have put in about $3.5 million into this idea. The investors include Index Ventures, SV Angel, First Round Capital, Betaworks, Jason Calacanis, Steve Case, and Jeff Jarvis. Danny Rimer of Index Ventures has a board seat at Tweetup. [TechCrunch]