R.e. the American calls installed on the system ... If you buy from BFC they'll swap the calls from U.S stuff to U.K. stuff for you if you ask, and is F.O.C. (as long as the caller works from an SD card).
Also .... If you do end up with U.S. calls on your caller, BE CERTAIN to turn the ruddy thing off when you pick it up ! Trudging back across the fields in the dark it's far too easy to accidentally prod or knock the remote, whether it's in your pocket or round your neck on a lanyard. Hit the right (or wrong) button and your careful and stealthy progress through the darkness will be disturbed by you shreiking like a girly and nigh-on messing yourself as a bloody wolf howls at what seems to be about a billion decibels from the top of your rucksack right behind your ears !
I refuse to answer questions on how I know this !