Especially since they were footing the bill for cell data with the early devices, it's hard to imagine they'd really want you to use it for Web surfing for sure. But the device also isn't very well suited to that.
I’d get voicemails (transcribed) and text messages to my Gmail and could text back from there. Gmail even had a lite version that worked quite well on the Kindle’s experimental browser. Fortunately, my needs for making/receiving an actual call on-the-go were nearly non-existent so it worked quite well.
Was really sad when they pulled the plug on the free 3G.