Dopplr has launched an iPhone app they are billing as a "social atlas". Curiously, and possibly wisely, you don't even need an account at Dopplr to use the app, meaning it will get exposed to a lot more potential users. However, a let down from the get-go is that you can't add upcoming trips from within the app right now, which is kinda the point with Dopplr, as it's users will attest. Hopefully that feature will be out soon. Till then if you want to add trips on mobile people can use the site, twitter, SMS or email in the usual manner, of course.
The app appears first on the iPhone, but apps for Nokia, Blackberry and Google Android platforms are planned. The app is available from the iTunes store here. But for Dopplr users it's going to be a real boon. The app puts the combined knowledge of your Dopplr network into an app which can tell your location, while allowing users to upload reviews themselves. There is also a built-in directory of city tips and advice. Plus, as usual, see where your network is about to travel to so you can plan accordingly. Users can also contact eachother directly from inside the app. There is plenty of content inside the app pulled from Dopplr's own content as well as your social network.
The question mark with Dopplr is how it will continue to fair against Tripit, which is tearing along at a fast pace and recently launched premium flight monitoring and alerts.