IPhone :: 3GS Navignon GPS App / How Not To Use Data Own Country

I am in Canada on Rogers, Basically,, they say that you can use Navignon's GPS all by itself while NOT using data. I wanted to get a practice run at doing this on my iPhone, because I am going to Europe where , obviously, I don't want to using my data. I know in Europe, I would turn roaming off. So my real question, is how do I really turn off my data plan at Rogers to try out of Navignon works on pure GPS? Turning off the 3G feature, I don't think would do the trick, and I tried going to Airplane mode, however that appears to shut everything off, including the GPS. PS I now have 3GS