Mobile system of Malaysia is GSM system, supporting to GPRS and 3G too.
If you are visitor from other country, and your mobile network provider is providing you the roaming service (some of provider terminate this service by default, please confirm with you mobile network provider before departure), you will be able to search and using one of the Malaysia mobile network upon arrival. The most probably is Celcom, Maxis and Digi.
There will cost you so much if you calling or answering calls, no matter a local or international call. You may consider to apply a prepaid card during the time you stay in Sabah. For more information, please refer to: Mobile prepaid card.