i jailbroke my all of my three previous iphones 2g, 3g and 3gs... and through jailbreaking i've completely lost visual voicemail and when i updated my jailbroken 3.1.3 3gs to 4.0 i lost the ability to send MMS and group texts, along with a plethora of cellular issues. After getting my new iphone 4 and setting it up as a backup of my (screwed up) 4.0 3gs i still lost the ability to send MMS and use VVM... after about two or three hours of tinkering around and moving and copying files from previous backups i now can use MMS... but no Visual voicemail
if i can get a guarentee that jailbreaking my iphone 4 will not get rid of any of the things my phone is SUPPOSED TO DO... then i may jailbreak.
(there are so many useful apps that are jailbreak only... but the main reason i'll jailbreak is for custom SMS tones)
EDIT:
Oh, and yeah i'm not going to jailbreak my phone unless there is a simple plug in and jailbreak option like blackra1n (for 3gs)
i feel like the pwnage tool takes too long (because it restores your phone... and re-populating my iphone with all it's music and movies usually takes about an hour and a half) and has a higher risk of not working