build.gradle(app) dependencies { ... implementation 'com.googlecode.libphonenumber:libphonenumber:8.12.6' ... } fun String.toNationalPhoneNumber(): String { val phoneNumberUtil = PhoneNumberUtil.getInstance() val locale = Locale.getDefault().country val toNationalNum = phoneNumberUtil.parse(this, locale) return phoneNumberUtil.format(toNationalNum, PhoneNumberUtil.PhoneNumberFormat.NATIONAL) } 단..