I feel pretty lucky I got grandfathered in on the unlimited data plan on my iphone. At least that is what they told me when I upgraded to the iphone 4 at launch.
I also only had to purchase a non 3G ipad and just the wireless one. Once jailbroken I can use my iphone as a 3g wireless router and...
I have been using the app called ....Friendly Facebook app.
It works great and actually a lot better than the one on my iphone. It was not free but well worth the couple of bucks I spent on it. I tried using the browser and it sucked but now with the friendly app I am a happy facebook user again.