May I recommend radios for staff members? It seems to work really well at Leprecon, and shouldn't be too expensive.
QUB Dragonslayers has 10 PMR radio units + headsets, which i should (in theory) be able to make available for loan to EirtaKon.
I know from experience that it is very valuable to have real-time comms between key staff members, especially in fairly distributed events. Mobiles help a lot for sure, but it's not the whole story. Radio systems are basically considered essential equipment for quite a few cons dotted around the UK.
(naturally there are other implementation issues with 2-way radio networks, but after Q-Con i'll be able to give a more precise evaluation of how effective they are ;)
Richard