I guess the idea is if mobile browsing takes off, and iPhone offers the best mobile browsing experience, sales would follow.
Maybe a lot of Blackberry users will want good browsing as well as corporate email and if iPhone gets that as well (maybe through a third party after the SDK is release) then there's more potential share gains there.
In other news, German and French telecom partners are reporting a rather high percentage of unlocked sales. But people are questioning Apple's strategy of limited distribution through exclusive partners:
http://money.cnn.com/news/newsfeeds/...2_FORTUNE5.htm