aGPS uses the location of the cell towers to try and triangulate your location. I don't know if this uses data however if you are using google maps, this will use data as the maps are downloaded from google once it knows where you are.

The safest bets to avoid any nasty shocks when you get home are to either turn data off and especially make sure that the phone has the data when roaming option unticked, completely disable your access points (delete them or add some **** to the access points to make them invalid access points) or see if your service provider has some kind of data roaming add ons though even with add ons with a data intensive phone like the x10 it is likely you will plough through the allowance on one of these in short time if you have lots of things set to poll in the background.

The final option to completely play it safe would be to either leave the phone behind or get a cheap basic phone which doesn't use data and take that with you

 

You can turn the data/internet receiver OFF on the phone in the same way you can turn off WI-FI and the GPS. Your phone then will only make and accept calls/texts! Nothing else! I will post the instructions in a second!

 

To switch off data connection, go to Settings - Wireless controls - Mobile networks - then untick MMS & Data.

Your phone will have no data connection until you re-tick the box!