Originally Posted by
gaelflyer
It really depends on whether you are arriving in Britain or Ireland first.
A prepaid Three Ireland SIM has a good deal on data and does not charge for roaming if you use the Three UK network.
...and if you arrive in the UK first, getting a SIM card from 3 will also allow you to roam in Ireland using your allowance.
#10 top-up will get you 500Mb which should be enough for 2 weeks of maps and light messaging. A
#20 top-up will get you 12Gb, which is more than you will ever need. You need to convert your top-up to and Add On in their my3 website in order to take advantage of the roaming, or they can probably do this for you in store.
Colm