How to use third party applications on iPhone legally.?

Question

I have just bought and iPhone and am worried about jailbreaking it incase anything goes wrong with it and it ends up voiding my warranty. I have heard people talking about an application apple are providing for around $20 which enables you to install third party applications, such as the NES etc. Does anyone know what this application is called? Also it would be interesting to know if there are ways of avoiding jailbreaks voiding your warranty?

Answer 1

its okay nothing really special

Answer 2

if you jailbreak it then installer/cydia are installed on your iphone which allow you to download 3rd party apps