hi, im not living is usa and i wonder if iphone 4s sprint unlocked will work on all the gsm operators in the world, or it is not for gsm at all and is only for cdma 
Yes it will. It can be unlocked for international use on GSM networks
This. Out of the box I don't believe it will work: You have to contact Sprint Customer Service first and they should unlock it for you.
yes but if it is unlocked from sprint? can it be used for gsm?
Only internationally. It would not be able to be used with AT&T.
that is strange, why i cant use it for at&t if i will be able to use it for t-mobile or some other carrier
It wouldn't be usable for T-Mobile either. If you have an unlocked Verizon, Sprint, or C Spire iPhone 4S they would not be able to be used with any U.S. GSM network service provider due to carrier agreements between the carriers and Apple.
so not for U.S gsm network, will it work for any other countries gsm network excluding U.S?