Consider for a moment that the DPI of the iPhone's screen (~160) is extremely close to that of the popular Kindle ebook reader and the Sony PRS-500/505/700 ebook readers (~170).
As a person that's done a fair amount of design work, 160dpi is MUCH more than sufficient for small legible text. Ysss is right, if there is a threshold, the iPhone's dpi is above it.
I'll bet that the computer that you're working off of has something closer to 80-140dpi, and I'll also bet that you have no trouble reading off of that.
}:^)~
Yes, text is readable at 160 dpi and you can read on your computer screen, too. But the 770 with 225 dpi was the first device where I actually enjoyed reading books on. I hate reading books on the computer. And reading on the G1 wasn't comparable to the 770, too. Now the screen on the N900 is even better than the 770 for reading books.
Tidings - RSS and Podcast aggregator for Jolla - https://github.com/pycage/tidings
Cargo Dock - file/cloud manager for Jolla - https://github.com/pycage/cargodock