c:\@Work\Perl\monks>perl -wMstrict -le
"my $dest = q{UK Mobile - Vodafone [GBRVF] [MSRN]};
 ;;
 my @xlate = ('', '_');
 ;;
 $dest =~ s{ \W+ (\w+ \] \z)? }{$xlate[! $1]}xmsg;
 print qq{'$dest'};
"
'UK_Mobile_Vodafone_GBRVF'