iPhone Dev Team member musclenerd has been working on an iPhone 4 carrier unlock for quite some time and has now updated that the progress is steady, updating eager iPhone 4 users waiting for an carrier-unlock he tweeted :

Steady iPhone4 unlock progress with @planetbeing...custom "pp" command to dump thread priorities: http://is.gd/dirUZ

After getting success in jailbreaking iOS 4 there is another interesting development from iPhone Dev Team member musclenerd, few hours ago he tweeted confirming the upcoming final version of iOS 4 as unlockable even on the newer Baseband v 05.13.04, also pointing out