Best thing I did was to jailbreak my phone and iPod touch. Free apps, utilizing everything your phone is capable of is awesome. Cons are sometimes your phone crashes, long download times compared to the app store on iTunes and yes you void your warranty which to me is fine. I never really noticed any battery change due to jailbreaking but I guess you never know. Bottom line is it is worth it to jailbreak IMO
Jailbreaking your iPhone will give you unlimited access to your phones functions and services. However, jailbreaking will ruin your phone's warranty. This can also affect the battery life among other things.