I have never updated my iPhone software, version is 3.1. So I tried to update officially via my iTunes to offered version 4.2 and failed due to error -402653138. What should I do now? Thanks in advance.
I didn't think the original iphone 3G was able to run ios4…? Have you jailbroken it into thinking it is able to? That might explain the fact that it cant actually upgrade...
The iPhone 3G was supported up to iOS 4.2.1
As for the first iPhone (original) you are correct that its support was dropped after iOS 3.1.3
My first guess would be either some connection problem to the iTunes servers or maybe a damaged iTunes installation. I think the best place to start is to download and install the latest iTunes version and try again.