If my iphone is factory reset is it unlocked to use on any gsm network?

Factory reset my iPhone 4s want to now if i travel will i be able to use Sim cards from other GSM network

Umm no…

factory reseting a phone, ANY PHONE, ANY DEVICE, means you wipe All USER DATA off the phone/device, so it acts/looks like day 1 when you first touched the phone/device. All your contacts/pics/music/apps/etcetcetcetc will gone, wiped, nada, zilch, el numero uno, do not pass go do not collect $200… Factory resetting has NOTHING to do with unlock a phone/device

If you want to UNLOCK an Iphone, call your wireless carrier to see if they participate in Apple's unlocking program (only if your no longer on contract)… If not, jialbreak your iphone, and get a simple unlocking app from cydia