I need to determine at startup what country a user is in, for an iPhone application. Presumably I will have to turn on location services and do some sort of reverse geocoding. I don't really want to use a third party web service if possible, are there any other suggestions for determining country from what location services provides?

Initially, I only need to check whether the user is inside the US or not, but this may change in the future to add more countries. I understand that location can not always be determined or the user may have location services turned off. Basically, I just need to know if the user is detected as being inside the US, in order to turn off a specific feature.