iphone 3gs old or new ??

[gritts]

hi,ive purchased an iphone 3gs and i want to put the jailbreak on its 4.2.1,before i can do this it asks if it the old 3gs or newer one how do i tell ??

white iphone 3gs 16gb

seriel no is 8895185w3nq

i read somewhere that it tells u in the seriel no

any ideas please ??