I bought a phone in australia and am now using it in ireland. the mobile data is set for australia's servers?

[Paulo]

Is the phone locked to particular network?
Try a three network shop as they also have three network in Australia, in fact they have three networks in 7 countries and as far I know (but better if you 1st check) I think you can use your national data allowances while roaming in any other of those 7 countries where three is present, so I suspect they should be able to help you, in fact if you buy a three sim in Ireland and top it up with 20 euros you will get unlimited broadband for 30 days + you still have the 20 euros left to use for something else.
If you already using a three sim from Australia then is quite possible the internet traffic is being routed all the way to Australia and back, making the internet connection quite slow, check your ping to see what is going on.

If is a signal issue, while I don't recall the name there is an android app out there which can help you manually temporarily change the type of connectivity, e.g GSM/3G/4G/etc

Good Luck!