Unlocked

Unlocked How can I check if my (unlocked) phone will work with a particular country's SIM cards, for 3G and calls?
How can I check if my (unlocked) phone will work with a particular country's SIM cards, for 3G and calls?
Can an unlocked phone be used in any country?Can you put any SIM card into an unlocked phone?Will my SIM card work in another country?How do I know if...