There are a couple of ways around it, one is to jail break your iPad (if there is a current jail break available) as I believe you can bypass the 20MB limit. The other way would be to buy a mifi unit, off of somewhere like eBay, making sure its unlocked and transfer your data plan into that. I use a mifi and, of course, the iPad sees it as a wifi signal even though it's really 3G and as such doesn't limit me at all.
The Archangel