curious about this as well for this reason. I purchased the app when it first came out, before there was ever any way to purchase specific regions, so I own the entire North American/Canada maps. I'm driving to Toronto from NYC next week, and just realized that the app will only be worth me using until the time i get to the border. after such time i may have to switch to old school maps b/c there's no way i'm going to allow my phone to incur roaming data charges while driving in canada.
however i'm also wondering if b/c the maps are stored on the phone if I will possibly still be able to use the app..although my guess is no...
I was searching for the answer to this question as well...because I upgraded to iP4 and gave my mom my old iPhone 3G; she got $15 (200 Mb data) and didn't want to use much. BUT she loves the NAVIGON app.
I have found that if you OPENs Navigon app, it will use a 'little' bit of data to locate you, then no more--just the stored maps. (However, if it looses the GPS signal, it will try to relocate you again.)
So, I did a test on her iPhone 3G , and drove around using NAVIGON for 4 miles:
Started with 252 Kb. After 4 miles, it ended with 274 Kb. (NOTE: Kilobytes!!)
good analysis, i never was quite sure how much data for the A-GPS (assisted GPS) approach the iPhone uses; i assume that's what it's doing ... not much
additionally, i did a test by swapping SIM cards w/ one of my kid's phone where i've turned off data service completely to the SIM card w/ AT&T (so no data charges ever) ... and even w/o data service turned on, my old 3G phone gets a GPS lock, a little slower w/o 'assist', but still achieved a lock.
to round out the topic of data use (beyond Navigon app) ... another important thing to be aware of is that some Satnav Apps are 'onboard' others are 'downloaded' during use ... so apps like, Navigon, TomTom, etc download all the map data when you install the program, and technically, don't need data service during use (other than assisting w/ GPS lock, or if you subscribe to live traffic service) ... and there are other Apps that download map data ongoing while use like Motion X or MapQuest and require more data during use.