I use following procedure for offline browsing of maps in my mobile phone. So you will not pay for gprs.
Download and install Mgmaps into your mobile phone. http://www.mgmaps.com/download.php
Generate map info from this site http://map.outdated.info , you will use map file in the next step.
Download and install mapmaker for creating maps http://www.mgmaps.com/gMapMaker-setup.exe , select map file you created, use proxy option.
Copy files which created to your sd card. configure gmap settings for using offline content.
If you have gps module, GMAP supports gps.