Probably the most important spec is the screen resolution, this has not changed in any version of either the iphone or the ipod touch.
480×320 pixels
All following details where taken from the apple page at: http://www.apple.com/iphone/specs.html
Display
- 3.5-inch (diagonal) widescreen Multi-Touch display
- 480-by-320-pixel resolution at 163 ppi
Size and weight1
- Height:
- 4.5 inches (115.5 mm)
- Width:
- 2.4 inches (62.1 mm)
- Depth:
- 0.48 inch (12.3 mm)
- Weight:
- 4.8 ounces (135 grams)
Audio playback
- Frequency response: 20Hz to 20,000Hz
- Audio formats supported: AAC, Protected AAC, MP3, MP3 VBR, Audible (formats 2, 3, and 4), 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