How to safely unlock my iPhone 3GS made in the 46th week of 2011?

I've already performed an untethered jailbreak using red snow

The safest way will be to get a proper factory unlock either directly from your carrier or from one of the big online vendors like http://www.cellfservices.com/ as this will stay even if you upgrade iOS and you won't have to keep using dangerous jailbreaks that might brick your phone permanently.

We provide an AT&T Official, Permanent, Apple unlock that remove any network restrictions your iPhone may have by marking your handset as unlocked in Apple's IMEI database. We provide this unlock for all iPhone models running all firmware versions, and there's no need to jailbreak.
You can safely update the OS on your handset at any time, and sync your device with your computer without fear of Apple removing your unlock
http://attiphoneunlocker.com/

You can unlock I-phone 3GS easily using Remote Unlock Service. Visit the site http://www.prounlocking.com/apple-iphone-3gs/rs8wp9/ get remote unlock service at reasonable cost and unlock it from service provider lock. I have unlocked my phone using this remote unlock service. In this method you need Jailbreak your i-phone 3gs.