I have an iPhone and I want to jailbreak it, but I have heard that the battery and the speed goes to sh%t if you jailbreak it.

All I want to do is get all the apps I want for free, like Tom-Tom and the internet share app.

I don't even want to change the background or ANYTHING else.

About how long will it take to jailbreak my 3.1.3 iPhone, and also will I run into any problems?
Will the iPhone die quicker?
Will my warranty be voided? Can the warranty problems all be solved by just restoring to factory settings? Is there a way for Apple to find out that you jailbroke it if you took it to the apple store if it crashes or something?