iPhone as a modem?

[The_Abyss]

As the title really. I used to have an HTC Touch HD and this was easy to use as a modem - same with my old LG Viewty. O2 would sometimes get a bit annoyed about it (write a letter if useage was too high) but otherwise it was fine.

Is it possible to do the same with an iPhone? I'm looking at the new 3GS.

 

[The_Abyss]

Thanks chaps.

If I'm right, I can then buy a PAYG one and use my existing O2 contract on it fine?