The flight sounds a lot like the Eye in the sky type, suggest you give Capital Radio in London a call (that is the only operator I know of in the UK) and ask who operates their flights and what they use for communication. The advantage with using a mobile is that a hands free kit with two earpieces will allow a two way with one of the punters on board (one earpiece for you and one for the punter, both of you using the hands free mic) If you go down the mobile route bring a selection of phones with you so that you have at least one on each network that is available in Ireland. At 1500 feet you are well within the the limits for using a mobile, how about a quick "jolly" to check how things work out, I'd guess you are using Aer Arran, so why not buy a ticket to the UK so you can see what works? (Making very sure the airline and crew are OK with this)