So I have recently started to design layouts for smart phones, clearly it is a different world from web design. One thing that struck me was the resolution/pixel density seems to vary depending on the handset in question ranging from 150 to 300 ppi. While looking around I could not find any one source of data for a mix of handsets so I thought I would start at list. If I miss any (and I will) than please feel free to add to the comments section
iphone
160 ppi
3.5 inch
480 x 320 pixels
itouch
163 ppi
3.5 inch
480 x 320 pixels
HTC Touch Pro
287ppi
480×640 pixels
Palm Pre
3.1-inch
480×320 resolution,
186 ppi
ipad
9.7 inch,
1024 X 768
(132 ppi)
For furth reading you might like to see this.
You might also like to try this pixel calculator.
If you have details from other phones please add in comments and I will update the post.
Tech talk and my thoughts 