First, I do not know how to active the G2 with a SIM, or via Wifi rather than via APN. (I'm trying to do the same thing myself at this time, and still seeking the solution).
BUT... I have found a baby step. I see that when you turn on the phone, it comes up to a starter screen which shows you the green Android, and the two selections, Emergency Dial, and, Change Language. I find that if I click on the "MENU" button, it pops up a tab at the bottom of the screen that says APN. This allows me to change the APN settings. Worthless without SOME data plan, but, it might be helpful to someone trying to use an alternate provider's APN settings (along with a SIM sled / flexible PCB (sold on several sites) behind the SIM to 'unlock' use with an alternative carrier, such as AT&T - easier to borrow an iPhone SIM with a Data plan, as there are more of them). Just a thought.
Just a note, I have already changed my phone from "Donut" to "CupCake", and my goal is to go to "Root". My current HBoot is 1.33.0006 (my phone has the 32B motherboard).