I'm a Verizon Wireless subscriber and G4 iBook user in Washington, DC. If I need Internet access while not at home or work, it's usually pretty easy for me to find a hotspot (free or paid at one of the 10^9 Starbucks within half a block from my house).
I used to have a Treo 600 with the $40/unlimited PDA plan, which I could synch using iSync. Although I used it, I didn't see the value added for my needs. Verizon charges up the a$$ for data services as compared to Sprint (or T-Mobile). Their cellular coverage is probably the best in the area, though. Now I have a RAZR, which is a really sweet phone (can also sync with the iBook but I haven't gotten the USB cable yet). No longer have any data coverage except for the $5/month WAP which I use in case of an emergency.
My point in all of this is that you should ask yourself whether you really need Internet access through your wireless provider if there are accessible and cheaper methods such as WiFi. If yes, I would consider those instead and not worry about having to go through your provider.