Iphone 3gs not working in South Korea

[Sweetrevenge]

Hello, I recently purchased an Iphone 3gs and moved to South Korea. There, I purchased a prepaid SIM card and put it into the phone, but its stuck on 'searching' and I can't make or receive any phone calls. I thought the Iphone 3gs was compatible with the South Korea frequencies? I recently Jailbroke and unlocked it so that shouldn't be the issue.

 

[Sweetrevenge]

I'll go into more detail of what happened. I bought an Iphone 3gs in America and brought it over here to Korea. Here, I realized the phone wasn't even unlocked so I went ahead and jailbroke it and installed Ultrasn0w which is supposed to automatically unlock it. The install was a success and when I looked under carrier, SK Telecom 14 shows up when originally only AT&T would show up. So I thought I could use the cellphone finally but apparentlyin the upper left hand corner I get a "no service" message and when I go under the carriers menu, there is nothing there. I tried turning off 3g and tried downgrading the IOS but nothing is working and I'm at a loss here. Isn't the Iphone 3gs supposed to be compatible with South Korea's frequency?