Finally apple is going to release a decent iphone firmware. With the iphone 3.0, you can copy & paste, you can use bluetooth for some things, you can send mms, and some other things.
Dev-team has said that the iphone 3.0 firmware is unlockable, you can jailbreak it, or unlock it, but they wont release a tool to do it for now until its officialy released. They just give one advice, dont upgrade your iphone 3g with the firmware 3.0, because it will update the baseband and the yellowsnow app will be useless. Be patient and wait for a custom firmware or for a newer version of yellowsnow.
When the iphone 3.0 is released, i will post here step by step, how to upgrade your iphone to the 3.0 firmware, and how to unlock/jailbreak it.

update: the iphone 3g s is going to be released on 17/6/09. When the dev team posts a guide to unlock it, you will find how to unlock the iphone 3g s here.