Can't sign up from a U.S. phone – NAVER Map, Navigation Review

I am visiting Korea from US. Google map doesn't work well here. On recommendation of Koreans, I just tried to sign up but it keeps complaining that "the country code of the phone number does not match the country information of your IP." Of course, it doesn't match because my phone is from U.S. and I am using WiFi in local hotel. Why should it matter?
Review by newman9999999999 on NAVER Map, Navigation.