This one - 6.1.0 (5 GSM+CDMA): iPhone5,2_6.1_10B143_Restore.ipsw

Once you've downloaded the ipsw, you should verify the file's integrity to make sure that the download was not corrupted during the download. You can refer to http://theiphonewiki.com/wiki/Firmware#Global_model_4 for the SHA1 Hash. You can use HashCheck or any other 3rd party tool to get the SHA1 hash of the ipsw.

This post has been edited by systemX: Jan 30 2013, 11:58 AM

After updating to 6.1, I still have to restart the phone to get the 3G signal back after I exit the lift. Disabling and re-enabling cellular data/3G/airplane mode did not help either, only way to get it back is to off and on the phone back. Faced this on 6.0.1 as well.

Just called Maxis, and the person over the phone told me that they are having reception issues with the nano sim and are still working on it. The workaround for now as suggested by the person would be to just restart the phone (for my case) or call them and get them to refresh my network location.