I think appstores really makes a difference in determining longevity of a mobile platform. In the case of iPhones: you can get first gen phones for less than $200 and it will still run all the latest apps released in the AppStore today;

There are plenty of useful apps to turn the handheld into a useful business tool (analytics, reporting tools, etc), data entry points (order taking, etc), point of sales system (even able to read credit card's magnetic stripe), and so many more - to keep it relevant and valuable for years to come.

I wonder what are the numbers like for older symbian phones?