Blackberry's became very popular due to the push email service and many companies providing them to employees (so they can be at their beck and call 24/7). However, they are now even more popular because people use them to send free IM messages. Mobile phone companies also provide a blacberry tariff which gives unlimited access to push email and unlimited internet browsing.

Why isn't there the same with Nokia?

Why isn't there an IM service which allows you to chat with any of your friends that has a [compatible] Nokia phone?

Why don't mobile phone companies provide unlimited internet browsing on Nokia phones like they do with blackberry? They say it is unlimited but it is really limited, to as low as 500mb a month, but with blackberry it's really unlimited. Why the difference?

I am very happy with my N900 (will be even more happy if the phone functions are brought up to symbian level) and it has removed the need to carry a separate mp3/mp4 player. But I may have no choice but to get a blackberry as well cause all my friends have blackberry for IM chatting and because I want real unlimited internet access.