The limitations of the iPhone when compared to a DSLR, I’ll list all the ones I can think of.
1. No interchangeable lenses
2. The user can’t control/adjust the shutter speed
3. The user can’t control/adjust the aperture setting
4. Small sensor limits the ability to produce quality prints larger than 8X10
5. Image quality degrades in low-light situations
6. Only 5 megapixels
7. No on-camera white balance control
8. No IS.
9. The iPhone4 has a 5x digital zoom slider.
However, if you use a digital zoom you will lose image quality, and the iPhone is equivalent to a 28mm wide angle lens on a 35mm camera.
If people want to buy & use the iphone that's fine but you are not going to get the same IQ found in a DSLR print, the world of photography is not a P&S or iphone it's a DSLR world. IMO i only use my phone to talk on that's what it was design for the iphone is only good for email and websites photos no bigger then 8x10. compare with DSLR Raw 5184x3456 print.
Also iphone camera was only design for people who love Jpeg