Can I use a Gibraltar mobile as verification number?

I recently moved from the UK to Gibraltar. I have my old UK mobile number as the verification number for my iCloud account. I want to change this to be my Gibraltar mobile number. If I go to System Preferences > iCloud > Account Details there is a dialog box with a drop-down menu to select a country. Unfortunately, Gibraltar isn't one of them. Is it possible to use my Gibraltar mobile? If not, will I run into problems if I don't have a valid verification number?