I have a iPhone 2G 8GB with restore error 23, I simply opened it up and disconnected the communications board from the motherboard, Restored it successfully on 3.1.3 and reconnected it once done, And works fine, Have been using it for 1 1/2 years since.
I love the 2G, Even though its old, Its so durable. I like mine because its in mint condition, However i am also using a iPhone 4S :)
Hope this helps people.