I recently picked up an old 3G Iphone for cheap. It is unlocked and on a carrier I use. I just want to be able to add a few apps and some games with cydia/installous.

I have done some reading. I am somewhat confused by the firmware/modem ware.

Currently the phone is @ 4.2.1 where as my modem firmware says 05.15.04

I get confused at this point as I am not trying to unlock my phone, as it is already unlocked and on the carrier I want to use (The phone works fine as is)

I have tried redsnow 915b3 version - it seemed to work fine - Cydia was installed, but each and every app and game I downloaded/installed gave me the "failed to install ipa" message.

I then moved on to Greenpoison RC5b2 version. I cannnot get it to install. It fails and tells me to retry each and every time I run it. I also have to reset my phone to factory each and every time I run this.

Right now the phone is taking a real long time in sync mode (as I set up the phone as a new one in Itunes by mistake when I had to reinstall the firmware after greenposion corrupted/failed on me.

Do I need to take the phone to the ipad firmware 6.15 in order to just jailbreak and use games/apps from Cydia? Or do I just keep trying with Greenposion or similar?

A little confirmation by someone more knowledgeable perhaps point out what my next step should be?

Thanks for any and all replies in advance.