or you could ask o2 to disable data roaming and only allow voice roaming on your number, not sure if they would do this for you. I know Voda do.
Or you could find out if 02 has any roaming agreements that don't include data with networks of where you're going and manually force your device onto that network.
Both of the above are just workarounds really but will mean the device can only pick up GSM and therefore won't rack up any data charges.
the ideal solution is to run with the latest OS which gives you the specific option to disable data connectivity while roaming.