Echofon, which used to be called TwitterFon, is used by over 3 million people. The startup offers a Twitter app for the iPhone, a native Twitter clients, a Facebook app for the iPhone, and a Twitter iPad app.
One of Echofon’s most compelling features is that it can determine which Tweets you’ve already seen between your mobile apps, so you don’t end up rereading the same content.
PostUp, which was incubated by idealab, opened registration for its bidded marketplace for real-time search last year and along the way has acquired a number of Twitter clients. The startup recently bought Twitter Android client Twidroid and news aggregator service popurls. PostUp’s search algorithms and marketplace has been integrated on a number of sites, including here at TechCrunch, Topix.com, and Businessinsider.com.
PostUp plans to expand the features and functions of EchoFon and says that the developer’s offerings are a “natural complement” to the company’s Twitter app for Android phones, Twidroyd.