Im not sure what you mean by installer but I assume your talking about apps. If you want to install apps you can download them from the app store and it will automatically install.Or you can download on itunes and sync to iPhone. If you have jailbroken you need to install 'installous' on cydia by adding hackulous as a source . Search how to install installous. For a normal iPhone that hasn't been jailbroken you don't need a extra program. But for jailbroken you need installous. I work for apple California i would know Also don't jailbreak it messes up your iPhone slows it down and voids your warranty.
Yes, when you jailbreak your iPhone it can still do everything it could before the jailbreak. A jailbroken phone only allows you to do more. You will have a second app store known as Cydia that allows downloading of apps that are not approved by Apple for various reasons. These include apps to change themes and fonts on your iphone. Also apps for wifi tethering are available.
yes jailbreaking your Iphone/Itouch will not ever break the devices. the only difference with jailbroken iphone is that you have access to "Cydia" which is an app store made for apps that are not allowed on the Apple App store. I highley suggest using GreenP0isen.
You don't need to be jailbroken now that the iPhone supports most carriers. The iPhone 4 is physically unable to switch from GSM to CDMA carriers anway.
No
The app that you are trying to open may not be compatible with your version of iPod Touch software.For example, if you have the iPod Touch 3.0 software, a lot of apps will not work with it because the apps are not compatible with that specific software.Some apps state in their summary that it isn't compatible with certain iPod Touch software versions.
ive seen one or two for the iphone but there are weird concepts like ur ipod has to be "jailbroken" amd such u can try them but dont be surprised if they dont work
No
if you bought if with orange or have jailbroken and unlocked it then yes is should work fine.
yes, but not all iphone 4 apps are available on the iphone 3gs/3g/2g becuase they are too high resolution apps, or need a front facing camera.
well it depends if you're getting the apps from the appstore or on your computer, if you are syncing from your iphone then u should try to sync from your computer and if that doesnt work then maybe take it back to the store and ask the experts...hope it helped!
Yes!!! :D Japanese iPhone apps work on English iPhones, but if they haven't set it up for English as well as Japanese, all the text will be in Japanese.