There are some options... just put together a solution for my wife using a wifi router from clear which works with both the itouch and ipad plus it gives them direct access to files on any microSD card.
I have a writeup with details at
http://BevHoward.com /iOS.htm if interested.
Additionally, when researching this I found several USBmodem/router options that have the ability to use a usbmodem with a usb wifi router to do the same. The issue that lead me to clear were the "plan restrictions" that ended up expensive and unreasonable for us since we don't have a standard "voice plan"
Note that while clear provides 4G to the itouch and ipad, coverage is limited and only within the usa, but they do provide sprint 3G "fallback" when clear is not available.
Hope that this information is of value.
Beverly Howard