It can be 5.0.1 or 5.1, as was mention it is really a luck of the draw here. When you purchase an unlocked iphone, it can either come 5.0.1 or 5.1 depending on which apple store you go and what is in their inventory. If they still have any stock left that we received before 3/9/12- 3/17/12, it's likely that it will be 5.0.1. However, because Apple receives shipment daily (except Sundays), the chances that of getting a 5.0.1 is slim as day goes by.
5.1 was released on 3/9/12 (a month ago). on 4/8/12 I went in and purchased an unlocked iphone from the apple store, it came with 5.0.1. Actually I purchased an unlocked iphone on 4/6/12 but because of yellow tint and light bleeding, I went back to the apple store to return/exchange it. So I ended up exchanging for a brand new unlocked iPhone. Both of them came with 5.0.1.
Oh not to mention the unlocked iphone that I purchased on 4/8/12 was produced on Week 6 (February).
Personally I would visit this site, it is pretty accurate.
http://www.chipmunk.nl/klantenservice/applemodel.html/
If I'm right, you can type in your serial number without having to open the box and still in it's wrap, type in the serial number, hit enter and it will tell information about that device, when it was produced, where it was produced, etc.
Name: iPhone 4S
ModelCode: iphone_4S
Group1: iPhone
Group2:
Generation: 6
Machine Model: iPhone4,1
Model introduced: 2011
Production year: 2012
Production week: 6 (February)
introduced test: GOED
CPU speed: 800MHz
Family name: Become a pro user to see this information. (sorry)
Screen size: 3.5 inch
Screen resolution: 960x640 pixels
Colour: White
Capacity: 32GB
Factory: DN (China, Chengdu - Foxconn)
