How can I unlock an iphone?

Open iTunes and connect your iPhone up with the USB cable When your iPhone appears in iTunes, click it.Click 'Restore iPhone' from the 'summary' tab.If a software update is available for download, you'll be asked to install it. Select 'download and update' (it'll save having to do later).This one's important; make sure you select 'back up' (the order of options varies between Mac and PC):Click 'Restore' to continue. If you're updating your software as well, it'll be labelled as 'Restore and Update'. Wait until the restore is complete, do not disconnect your iPhone. This may take a while (over 30 minutes isn't unusual).Once your iPhone has been restored, it'll automatically restart. Once your iPhone is back online, disconnect and reconnect the cable for iPhone for it to be recognised by iTunes again.
Select 'restore from this backup' to reinstate the backup you did earlier.It will take a short while for your backup to be restored to your iPhone. It'll restart again, keep your iPhone connected at this time. Once your iPhone has restarted it should be unlocked.If you're prompted to update your carrier settings, click 'update settings'.Sync your iPhone with iTunes again to restore you apps, music and other iTunes content to it.