way to turn off or disable network conmectivity to avoid getting roaming or data charges while going abroad while keeping wifi enabled ( to use with imessage and other applications)

I am going to new-york and i want to be using my iphone, but i dont want to pay fees linked to international roaming and such.

I still want to use wifi to be able to browse and such on my iphone...

Thanks for helping me.

I have an iphone 5 running ios6.1