I just got this iPhone, and I can't download not one single app. This is very nerve wrecking,
What are you trying to download? Depending on the app, it may no longer be compatible with the 3G iPhone.
Well, that phone has been discontinued for years. Time for a model developed this decade.
Here are some tools to search for compatible apps (The first one is my recommendation).
iOSSearch - Find apps in iTunes for iPhone 3G, iPod Touch 1st, 2nd gen, iOS 3.1.3, 4.2.1 etc.
Vintapps 3.1.3 - paid iOS app for finding compatible apps.
Apple Club - filter apps by iOS version.
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