Just booked an internal flight from Miami to Jacksonville with American Airlines over their web page. You simply go into their worldwide site proceed as normal and prior to the payment phase select 'hold'. Once you have held the reservation you phone thier Dublin office and they will complete the payment process. Simple enough really. Pretty cheap too! Incidentally, their Irish webpage will be up and running in July when it will be possible to run through the whole system without the need for a phone call.