If i buy the iphone 6 with a contract of $299 USD can i unlock it for international use?

Will it be cheaper than buying the factory unlocked from T-mobile instead of paying $750 USD?

Sure you can unlock the phone and use with any carrier worldwide. But you'll have to pay Early Termination Fee and Activation Fee and pay for one month which will take the price to the unlocked model. You'll also have to spend for the unlock so it will be like more. Another thing, T-Mobile sells contract-free iPhone not unlocked iPhone. Apple store sells those. You can find cheaper outside the carrier and Apple though. If you need unlocked iPhone 6 at reasonable price cheaper than retail, mail me.

Check with Tmobile. You can 'add' international packages to your plan with the purchase. Sometimes they hold you back 90 days and require a current bill, but they offer international options on their plans. Best luck.