Default [Q] No roaming option?

Hi, first post for years so apologies if I'm in the wrong section.

I'm in USA on holiday from UK. I have an old HTC Touch Pro 2 running WM 6.1. Data Connection is switched off as I didn't want to get any data charges abroad. But dismayed to discover that using Google Maps automatically switched it ON and I've been duly billed for the short time before I realised this. I called my provider, O2, who said I should switch off Data Roaming. But i can find no such setting!

Can that really be true? I though all smartphones had that facilty?

Terry, East Grinstead, UK