I wanted to get some movies onto my iphone without itunes, largely because I run linux at home. There are various ways proposed online - the most common being to mount the iphone as a storage device - but there's a very, very easy way: VLC.
- Download VLC from the iOS app store
- Get the device onto the same wifi network as your computer
- Open up VLC on the device, click the menu icon, and click wifi sharing.
- On the computer, use a browser to navigate to the shown IP address.
- Click the upload button, upload the videos you want.
That's it. Super easy, took a few minutes. Works on any major OS!