not sure what you mean by all this but As for tethering, are you asking how to tether?
i believe you can have EDGE as an option to a Voice Plan (AT&T) and not the other way around.
Any phones or cards (PCMCIA/express) that will accept the sim and play nice with EDGE over a tethering setup
By updates and downgrades, are you hacking your iphone and would like to keep the hacks and tethering?Knowing that I could just not upgrade or just downgrade to 1.0.2, but updates will keep coming and I would like to explore alternate routs to making net access available when needed with out constantly relying on others to update and repair.
Anyone have some good ideas or methods of dealing with the problem of updates?