I've tried the equivalent of using the iPhone for Internet access with the current-model iPod touch and did NOT find it a pleasant experience--it felt like using an iPad "writ really small." Particularly bad is Twitter and Facebook access with their official apps, where the text was difficult to read when displayed in portrait mode.
Small wonder why I have a Samsung Galaxy S III for my cellphone--at least the Twitter and Facebook apps are actually readable.
I don't have perfect vision but I certainly can read twitter or facebook apps on my iPhone 4S quite easily, and I usually have to read it from further than usual since the phone is hooked to my earphone and the cable is short, so I can't lift the phone much after taking it out of my pocket, so I read it while holding it near my front pocket. But that's facebook and twitter. I can't say the same for websites with no mobile version. Now those are a tough read, even if I hold the phone in front of my eyes. A lot of zooming in and out is necessary then, but a bigger phone wouldn't really help on that either. In any case I'd have to zoom in.