I turned off data and roaming the whole time. Just stick to texts (if you need to) and use Wifi for emails. You can get a data plan for travelling, but it's still a giant ripoff.
I unlocked my phone and bought a Sim for 15E then another 12E bought me 500MB of data. That came in handy and is a good idea if you are only in one country - but once I crosed the border, I was back on travellers rates. The good thing is once my 12E ran out, even on travellors rates, they can't charge any more since it was prepaid.