I have a blackberry 8700 that I don't have a data plan but I use on pay as you go and use google maps opera browser for the net.
I bought another blackberry for my wife exactly the same model but I notice it says GPM on the top right of the screen next to the reception strength meter and my phone says GPRS in the same area.
My wifes phone wont access the net and I am thinking it may be the difference between GPM and GPRS...