ios 4.2.1 app

Can you be more specific?

Many applications will reguire iOS 5 or higher nowadays. If you have an iPhone 3Gs, you can update iOS by plugging it into iTunes and checking for updates.

If you have an iPhone older than a 3Gs, then you cannot upgrade your version of iOS, and your only option is to buy a newer device.

Go here:

http://appshopper.com/

You can search for apps by iOS version, something you can't do in the iTunes app store.

There are actually a lot of games and apps which are compatible with your iPhone which runs iOS 4.2.1. You just need a tool to separate them from the incompatible apps.

Here is my favorite solution:

iOSSearch - search the iTunes store for compatible apps.

And here are some things other people have suggested:

Vintapps - paid app.

Apple Club - filter apps by iOS version.