First, let's get the features common to file transfer apps out of the way: With ReaddleDocs installed on your iPhone or iPod touch, you can swap files back and forth as though you're using a flash drive. ReaddleDocs, like many other file transfer apps, relies on the WebDAV protocol to share files with computers and devices via a Wi-Fi network. The protocol supports Mac OS, Windows XP/Vista and different flavors of Linux.
Like many apps — and not just file transfer apps — Readdle enables you to read and fast scroll through PDFs, JPGs and all the other formats the iPhone and touch supports. You can choose between portrait and landscape views, like many other apps too.
You can access Apple's MobileMe iDisk or any other Web storage site where you have an account. That's not unique. Quickoffice MobileFiles, for example, will do that.
If you and your iPhone or touch buddy are on the same Wi-Fi network, you can exchange files. Again, that's not unique. Hey Mac's Briefcase, for example, will do that.
Now, let's get to the features unusual for file transfer apps: ReaddleDocs comes with 512 MB worth of free storage and an email address on Readdle's Web site, which you can use as a briefcase to store and manage files and forward emails with attachments from your desktop to your Readdle storage email address and read them online. You can also forward emails from your Readdle account to anyone.
Readdle has built-in email and a Web browser. You can email a document as an attachment. One nice wrinkle: You can create a signature for your emails. Another nice wrinkle: You can zip your files.
The browser enables you to read Web docs in full-screen modes (the app's menu drop off the display), download open files from the Web and save them to your iPhone.
If you need more storage, ReadleDocs is available for a monthly subscription fee of $5 to $10. Box.net, from Box.net, also includes free storage — 1 GB worth — with its app. The problem is that you can't transfer files straight from your handheld to your desktop.
As I noted earlier, most file transfer apps use Wi-Fi to shuttle files from one place to the other. What makes Readdle truly unique is that you can also do the same thing over EDGE and 3G, which means you can send your files to Readle's server virtually no matter where you are.
Readdle has some other extra goodies: It also suports e-book formats: TXT, FB2, RTF and HTML and you can bookmark pages.
Last, Readdle is stuffed with help docs. Like so many apps in the App Store, it appears to have been written by a non-native English speaker and some passages are tricky to understand. In the plus column, this app is so easy to use, you probably won't need to read the docs.
If your main interest is moving files from handheld to desktop, there are several less-expensive apps than ReaddleDocs. If you need to access your files while on the go and like the simplicity of emailing apps right from the app, then Readdle will do a better job. "You get what you pay for," applies here.