I don't know about iPhones, but I'm guessing files are transferred to them in a similar fashion to iPod. I'm guessing it would be easier if you have iTunes installed so you can drag & drop playlists or files from one to the other. I'm guessing once you connect iPhone to computer a menu will appear when it starts to communicate with iTunes.

Limitations of files are as shown below:
Apple - iPhone - Technical Specifications

Audio playback
▪ Frequency response: 20Hz to 20,000Hz
▪ Audio formats supported: AAC (8 to 320 Kbps), Protected AAC (from iTunes Store), HE-AAC, MP3 (8 to 320 Kbps), MP3 VBR, Audible (formats 2, 3, 4, Audible Enhanced Audio, AAX and AAX+), Apple Lossless, AIFF and WAV
▪ User-configurable maximum volume limit

Video playback
Video formats supported: H.264 video, up to 1.5 Mbps, 640 by 480 pixels, 30 frames per second, Low-Complexity version of the H.264 Baseline Profile with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4 and .mov file formats; H.264 video, up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Baseline Profile up to Level 3.0 with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4 and .mov file formats; MPEG-4 video, up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Simple Profile with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4 and .mov file formats