I can't download any free apps from apple store on iphone?

I have a iphone 3g, ios 4.2.1, jailbroken and unlocked with redsn0w. I tried downloading free apps from app store, i sign in with my apple id, and then the app says waiting and then disappears? Can you guys please help me?

Its the fact that you have 3G, i'm typing with the same phone you have and had the same problem. Apparently the 3G isn't up to date with certain apps (usually all of them). I tried everything including upgrading my 3G to a 4G but its the device thats not worthy enough. Only way to get them apps is actually buying a 4s or 5, id say buy the 5 because when the 6 comes the 4s is going to have the same problem as the 3g has right now.

Recently, I found that app store is available on Moborobo. It provides free and paid apps/games. It works fine for me. You may have a try.
Hope it helps.