Factory or not?

[bytebak]

I saw an iphone in a pawn shop the a few weeks ago,3g,2.0 software,not jailbroken.I put my sim in it and bam signal,made some calls works great.updated to 2.21,booted the phone and again bam signal works great,i jailbrok it installed cydia,no prob.still works fine with the 2.30.03 baseband.how can i tell if its factory unlocked or yellow snow,will i keep the unlock with 3.0..i even did an erase all content on it.still go my sim in it and its fine.This phone is a replacement for the 2g i bought the 2nd day they were out.cant beat that for dependability.