Do you mean that the formatter must be 'currency' for it to work properly? I tried to do something like:

$.extend(true, $.fn.fmatter, {
amount: function(cellvalue, options, rowdata){
var op = $.extend(true, {}, options, {
currency: {
decimalSeparator:'.', decimalPlaces:2, suffix:'', prefix:', thousandsSeparator:',', defaultValue:' '
}
});
options.colModel.align = 'right';
return $.fn.fmatter.currency(cellvalue, op, rowdata);
}
});

so that I can simply use formatter:'amount' in colModel. I need to also specify an unformatter for cell edit?