Opting to build an app for Highrise due to customer demand, the 37signals team worked with Overcommitted (who also built Ember) to create a clean and simplistic version of Highrise for the iPhone.
The app is built around a great contact search experience and stores contact info locally (an initial lengthy download is required) to make the overall experience much quicker. The app also supports voice notes (with transcription possibility slated for the future), text notes, tasks and the ability to view e-mail file attachments within the app.
37signals spells out that this is just the first iteration, with future evolutions to come, but we still think that avid users of the CRM tool will greatly appreciate the introduction of the official iPhone app -- especially since it's free.