We haven't tested this ourselves, but Pyrofersprojects came up with an interesting, but ultimately impractical, way to turn your iPhone or iPod touch into a 3G internet-using device. All you need is a 3G smartphone with Windows Mobile 5 or 6, a 3G data account, and the know-how to follow a guide teaching you how to set up internet sharing over Wi-Fi. After that's done, you can use your iPhone/iTouch to go through your other smartphone (which costs probably as much as your iPhone/iTouch), in order to get online. It's pretty gimpy, but at least it's 3G—and the irony of having to use a WM phone with an iPhone isn't lost on us. [pyrofersprojects]
Here's an idea; someone should create a communication only 'radio' that does 3G. You stick your SIM card in it, do the whole WiFi networking thing (maybe automated if it's a commercial product) and have the all communications go through the 'radio'.
Maybe even something small that plugs into iPhone or that you can keep in your pocket (kinda like those tiny bluetooth GPS receivers)