I haven't seen it auto-detect in that way. The carrier list options change depending upon the country so really it needs to be selected first.
I found that if you enter the phone number and then change the country then Bango clears the phone number field and you have to enter it again. But possibly you are seeing different workflow because Bango can auto-detect your country whereas it cannot detect it from my IP.
Do you have the country string set correctly in the testvars file? If so then it probably shouldn't even reach this code block.