Open-source messaging service Funambol has a new contact-management app for iPhones that's the bee's knees. It works both as a Web app and a native application for users with iPhones that have been jailbroken and have the Installer.app loaded on their system. In its current state, a Funambol-registered iPhone can slurp up all your iPhone contacts and make them available for backup and editing online. You can then sync over the air at any time, to either recover contacts to your phone, or add news ones you've created using Funambol's Web-based contact manager.
In addition to contacts, the app has planned integration for calendars, to-do lists, and notes, all of which the company says should be on track for Q1 2008, as soon as Apple gives developers a higher level of access with their SDK.
To access the app, you've first got to go register with Funambol's myFunambol service and setup a user name and password. After that you can either visit the Web version at http://my.funambol.com/iphone, or install the app through installer by adding Funambol's iPhone page as a source (instructions here). Both apps do the same thing, so honestly there's no real reason to go through the effort of installing the app locally.
For Windows users, this is a far easier solution than dealing with Outlook's contact manager or having to bother with iTunes' less-than-steller sync speed. In my testing I found it managed to sync everything over in about 15 seconds over a Wi-Fi connection, and about 30 over EDGE. Interestingly enough, there is another app from Zyb.com that does the exact same thing, although I prefer Funambol for avoiding the whole social-networking angle and skipping straight to a simple contact manager. There's also Plaxo Mobile Plus, but that's not set up to run on the iPhone just yet. Expect them to launch a solution when the iPhone SDK hits.