I'm not sure that is how a serial works as that is a 3GS Model number, but if you count it yourself...
The 3rd character is a 3 which suggests 2003 or 2013. As 2013 hasn't happened I would assume 2003, however no iPhones were made in 2003
The 3rd number is a 0 (suggests 2000 or 2010) no iPhones were made in 2000.
That is why I strongly think that this idea of a production date being included in a serial doesn't exist in this form.
The other reason is that my iPhone 4S serial only has 3 numbers in it and is in this format A38BBCDEFGF2, this is totaly out of sync with all possibe formulas on iPhone serial number production dates.
My 3GS has 881270***
Under this principle the phone would have been made in 2011, I got the phone in late 2010 - it was a refurb, so I doubt that is the case.