I see a lot of you are for verizons 1GB for $20.00 plan. But since (as you said) I can easily change plans from month to month, I think I'll give AT&T a try.
I'm not sure if I am misunderstanding you, but be aware that there is a Verizon iPad and an AT&T iPad. Once you buy one or the other, you are locked into their network. You can't buy an AT&T one and later decide to subscribe to the Verizon service. You are stuck with AT&T as long as you own that iPad.
If you knew this already, please ignore.

Edit: I guess it would help if I read the whole thread before responding. I see Sandy already said the same thing as I just did.