You can rent a cell phone at various locations for daily and weekly rates.
You can also pick up a pay-phone card for about 5,000 Won at the little convenience stores and other shops. I always carried one of these in my wallet in case I needed to make a local call, especially in the event my cell phone broke, the battery died, or I could not get reception while traveling. These cards have little magnetic strips that remember how much cash you have left on the card and can be used for local or international calls. Many pay phone don't take change or only take 10, 50, and 100 Won coins, so they can be a pain to keep feeding.
For international calls, Korea Telecom is expensive, so many foreigners buy international phone cards. These are sold at a few shops in areas with lots of foreigners like Itaewon. Rates on phone cards are amazingly cheap, like 3-4 US cents per minute from Seoul to the US. If you buy a more expensive card (like 50,000 Won rather than 20,000 Won), the rates will be even cheaper.


