It looks like progress on Sparrow for iPhone, the Sparrow mail app for the iPhone, is moving along at a good rate. I posted around 6 weeks ago on this, and at that time the developers had posted an image of the app and a status bar showing it as 61% complete.
Now the image has been updated and shows it as 81% done. So if that status bar is a good indicator we may see the release of the app in the next couple of months or less.
Judging by its reception as a Mac app, I would imagine this will prove a popular alternative for the built-in Mail app on the iPhone; always assuming the iPhone version is a good one.
You can keep up with the latest and sign up to get an email when the iPhone version is released at this Sparrow page: http://sprw.me/comingsoon/
Any big Sparrow fans here anxiously awaiting the release?