If you don't have a data plan, and don't have data access blocked, then you will get charged for the data transfer that the GPS servers provide. This amounts to less than 5 kB each time you start up Ovi Maps, SportsTracker, geotagging of photos, or the built-in GPS app. Depending on your pay-per-use rate, this may be a few cents to several $.
Google Maps is a different deal, and will use a large amount of data since the map tiles are downloaded OTA and not stored on the phone.
If it's a concern, you should disable A-GPS and delete the server name from the Positioning server setting.