Can I buy and use mobile used in other country?

Depends on the phone, obviously. In the US some phones do not use technology that is widely supported. In addition, some of the phones may be locked to a specific carrier, requiring you to unlock the phone for use in Malaysia.

Lastly, your own carrier may have restrictions about what can be used on their network.

So you'll have to investigate all those things, but the short answer is that you can get a GSM phone, unlock it and use it most of the time. You can also get unlocked phones on ebay and other places.

Yes you can buy a phone use in other countries but you have to look at some of the circumstances that you might be facing. One is the compatibility. Before you buy, check if the cellphone is suitable with your carrier's system. If you're uncertain, examine with client support on both the owner and carrier's ends. Like for example iPhone. It is locked on a specific network only. When I bought mine and have to travel abroad, I have it unlocked from attiphoneunlock.net. Now, a new law is passed in the US making iPhone unlocking illegal making it more difficult but not really impossible.

Other factors you need to look at is the charger. Make sure it comes with either a Northern United states charger or adapter. Most imported phone especially in Europe have their own standard of chargers. Others might be GSM 850 Band and Data Coverage.

Yes you can.

Yes, you can use it in the Malaysia. US makes widely network supported technology. First you make this phone unlock then use in your country. Without unlock you can't you this phone in your country.