I believe some have commented on other threads, use the search function.
There are other threads for this
To answer your question: bad. Both devices don't get:
- Siri
- Panorama
- AirDrop
- Filters in Camera
- Translucency effects
The iPhone 4 will not get what the iPad 2 gets:
- Parallax
- Dynamic Wallpapers
- big screen
- Photo booth app
- dpi < 140
The iPad 2 will not get what the iPhone 4 gets:
- Phone, Stock, Weather, Compass, Calculator apps
- Retina screen
- small screen
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