In a reply to my previous post DM Osbon pointed out that Iphone users mainly browse text based web pages like blog readers and twitter. I googled around for more data and I was surprised with the results:
This survey suggests that 68% of Canadian Iphone users use less than 500Mb per month: 2009 Poll
Here is a description of a more recent Consumer Reports study that pegged typical Iphone usage at only 273Mb per month: Consumer Reports Study Blackberry users come in at a very modest 50Mb per month (unsurprising given the strong association between Blackberry and email).
I am quite pleased to see that my own mobile internet usage fits right into the consumer reports statistics as a user of an "other smartphone", average data 150Mb/month. I don't feel such a cheapskate any more for sticking with my miserly 250Mb data package.