I have a first generation iphone, I ahve 80 mb of internet usage a month. The problem I have is that the only time I can actually access the internet is through our wireless at home. Anywhere else and it says there is no connection. I have checked the settings and its all set up correctly. What I did when i bought it was put my old sim from my other phone into the iphone, but i could access the internet fine on my old phone!
You need to set the interenet settings on the iphone to match the correct ones for the sim account, these will be different settings to everything you find saying it's for the iphone because you are not using an iphone sim.