The recently released iPhone 3.1.2 update also includes a carrier update for AT&T iPhone 3G and iPhone 3GS users. The carrier is updated to AT&T 5.6. The baseband/modem firmware for the iPhone 3.1.2 update still remains at 05.11.07 (which currenty cannot be unlocked).

How to update iPhone 3.1.2 carrier settings

1. Download and install the iPhone 3.1.2 firmware to your iPhone 3G or iPhone 3GS.

2. Once the iPhone  3.1.2 firmware is installed, iTunes will display a message saying: “An update to the carrier settings for your iPhone is available. Would you like to download it now?“. Click Download and Update.

3. Once you’ve clicked the download and update button, iTunes will automatically update your carrier settings and display the following message: “Your iPhone carrier settings were updated successfully“. That’s it, you’re done!

I’m not sure what is included in these new carrier settings. Last time Apple issued the carrier settings to enable MMS on AT&T, maybe these carrier settings will enable VoIP over 3G, now that AT&T is allowing Skype to use 3G. What do you think?