There is an older thread about this at
viewtopic.php?f=1&t=31447&hilit=iphone but some things have changed recently and I thought I would start a new one rather than add it to the old thread.
On Feb 3rd Apple released another firmware update for the iPhone (3.1.3) included with it is another modem firmware update. Update any version iPhone to this and you will lose your jailbreak and unlock, or for now the ability to do so. This update really provided nothing of importance and it is thought that apple realized it to see what exploits hackers would find in it so they had a chance to patch them before the next iphone release & firmware update. As such an unlock and or jailbreak for this version will probably not be seen until summer when the next iPhone should be released. Unfortunately this update will start showing up on new and replacement phones pretty soon.
To make matters worse Apple on the above date stopped signing any firmware version except 3.1.3 for those who need to do a restore. Signing of the firmware before restore only applies to 3gs phones. If you have a 3gs phone, have previously jailbroken it and saved your shsh sig file on cydia, (clicked the make my life simpler bottom, on the cydia startup page) you are in luck and there is a way to restore your phone to the 3.1.2 firmware, preserve the jailbreak and unlock.
If you have a phone that somehow got updated to 3.1.3 via the official iTunes update you can't downgrade the modem firmware. Depending on the model you may be able to go back to 3.1.2 and at least jailbreak.
3gs - firmware can only be downgraded if shsh sig file for older firmware version was previously saved and / or phone is currently jailbroken
3g & 2g - as there is no firmware signing on these phones firmware can be downgraded by doing s shift click restore in iTunes.
IMO The best way to jailbreak an iPhone is via to tools provided by the Dev-Team (
http://blog.iphone-dev.org/) such as pwnage, etc which are all provided free of charge. Many people including myself have used Blackra1n, numerous people have had problems with their phones searching for carriers, loss of wi-fi, etc. As of late a number of people have reported phones locking up that were jailbroken with Blackra1n and having great difficulty re-storing them in many cases losing their jailbreak and unlock as they were forced to install 3.1.3 firmware. I had my phone lock up as others had. If you phone has been jailbroken with blacker1n you can redo it with the 3.1.2 version of the firmware via pwnage wiping out all changes made by blackra1n. IMO some of the phones locking up may be the result of not shutting them down and rebooting them for long periods of time (week or more)
In summary here are links to solid information on jailbreaking an iphone:
http://blog.iphone-dev.org/http://www.poorlad.com/iCommunity/http://www.hackthatphone.com/http://modmyi.com/I will be happy to jailbreak and unlock an iphone for any CRT brother (free of charge, liquor gladly accepted

) if it can be done. I am in CR frequently, and live in SW Florida.
Bill