Buy a calling card at a store on campus or at convenience stores off campus or you may use the public phone using some coins.
From Korea => Overseas: Dial 001 - (the country code you are calling) - (Overseas area code) - (Telephone No.)
From overseas => to Korea : 82(country code of Korea) - 51(Area code of Busan) - (Telephone No.)
From Busan => Other areas in Korea : (Area code : Seoul 02, Daegue 053) - (Telephone No.)
Other areas => to Busan : 051(Area code of Busan) - (Telephone No.)
The phone in the Students Dormitories is available to receive incoming phone calls only, thus making off-campus calls is not possible. You are not to accept collect calls. You can use the phone at no charge to call a number within the campus telephone system just by pressing the 4- digit number without exchange number.