phone data usage when connected to Garmin?

Has anyone used the Garmin 510 paired with an i phone? I am trying to find out how much of the phones data is used (in general terms)? I used google maps abroad last year and got a huge bill so am cautious connecting the phone to anything. None of the advertising mentioned the data usage and I know f all about this.
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Download navfree from app store, it is wonderful and has guided me round so many countries and always without hassle and cost.
"Thanks for the ride man, ive ad de time of maa life"