how i can know if my iphone 4s is factory unlocked

[gilyos]

hi all'

i just got a iphone 4s 32g from usa
the seller told my father that it's factory unlocked iphone
i leave in Israel and when i try to activate it igot a massage " you need to put the sim card that came with this phone...."
i don't know what to do 'i spend 850$ and i can't activate it
any suggestion?
the part no is MC921LL/A
i cheked and it seems (i'm not sure) that this part no is factory unlocked iphone ,am i right?
i got ios 5.0.1
my friend has a AT&T sim and when we try to activate it wuth it we can but when i put my local sim i get this massage again.

tnx in advance

 

[Jmills87]

Model number won't tell you if it's factory unlocked or not, but if it's telling you to insert an official SIM then it's not factory unlocked.