Jailbreaking does not affect your warranty if you need to take your phone away just do a restore using iTunes and your iPhone will be stock again(this is recommended anyway for privacy reasons), it gives access to apps that Apple wont authorize, utilities to hack or theme your iPhone, games etc and most are free.
No need to PM me, just post your questions in this thread and we'll help you out, also use the search function.
http://mybroadband.co.za/vb/showthread.php?t=100952&page=49
Click on my sig to get access to the Appstore aswell.
Again thanx. Will try it