Is iTunes the only way to interface with an iPhone on a PC?
I know of no other solution to sync the handheld device. 

If you want to get files on and off the device, you may be able to find tools/apps to help you. I've had to resort to a tool to get some audio and video content off of an iPod once that was loaded on someone else's machine; when you associate an iPod with a new machine, iTunes really wants to zap the contents, and I assume that may also be true with iPhone. 

Also, the way some of that content is stored on the device may not be what you'd expect (files in a file system), it's more like cryptically named blocks of data in a database. But there are tools that can help you deal with the problem.