Question about iOS6's GPS+Siri

[November's Chopin]

When using Siri with iOS6's Map, does it require a constant 3G connection (since there's no wifi while driving obviously)? Or no connection is required and it only uses cellular data? Or it will turn on data during the few seconds Siri needs it, then turn itself back off? I'm kind of paranoid about data fees now after being screwed big time with some ridiculous data usage amount that I have no idea where they're from in the first few months with my iPhone 4S, so now I pretty much never have data turned on.
Also, does anyone know how iOS6's Map compared to actual GPS apps for iDevice, like TomTom? Which one is more accurate/faster/more battery efficient? I know that TomTom only works for a few countries and you gotta get the app for each country, what about Map? US/Canada only or all countries?

[Teknikal]

I might be wrong and I'm sure I'll be corrected very quickly if I am but I think you are going to need a constant data connection, it's only very recently Google added offline mapping itself.