The major difference between an iPhone and an iPad is the size of the screen and the ability to act as a cellphone and folks who have bought both are finding that this may not be enough to justify having both an iPhone and an iPad.
Task | iPhone | iPad |
Read books | √ | √ |
Cellphone | √ | X |
Email | √ | √ |
Browse Internet | √ | √ (larger display) |
Add Additional Storage Capacity | X | X |
USB Port | X | X |
Connect to Internet via WiFi | √ | √ |
Print | √ | √ |
If you have an iPhone, you might consider deferring your purchase of an iPad-like device until major players such as Samsung and Blackberry unveil their offerings. It is possible that non-Apple iPad-like devices may have additional features that will make it worthwhile to purchase a different vendor's product.
Here is a an link reviewing non-Apple iPad-like devices:
http://www.wired.com/gadgetlab/2010/04/gallery-non-apple-tablets/all/1