Sathish, absolutely no idea about Nokia/Blackberry. I am only Android :D I suggest Android based smartphones becos they are much affordable and equally fumctional with iPhone. There simply is no alternative as of now, technically and feature wise.
This link also may help - http://www.letsbuy.com/advanced_sear...ywords=android
There is a saying that "Digital Cameras are not just MegaPixel, there is muchmore beyind that". Similarly, mobiles are not just hardware specs, there is another important thing called apps/ecosystem. Add affordability too and you automatically land on Android Smartphones.