I cannot talk about other mobile phones
but me and my friend have different Apple IPhones and it was really easy
to get a korean phone number for this three weeks. :)
So what do you have to do...
You have to have a free mobile phone
You have to buy a Prepaid SIM Card in a "GS25 Market" in Seoul.
"GS25" Market are everywhere in Seoul...Its a very famous supermarket-chain in South Korea.
But I warmly recommended to go straight to the GS25 at Incheon Airport or Seoul Station.
They will sell those Prepaid SIM cards. I bought mine at the market in Seoul Station.
You can ask the grocery clerk for this SIM cards and show them your phone..they will
know which prepaid card will be compatible with your phone :)
So very easy! right? ;)
After that... change cards and follow the instructions which you'll get with the card. :)
My provider in Korea was "Olleh", :D And i was deeply contented with it :)
Hope that was helpful for you ;)
♦ Me ♦