Actually, there is a way.
Then, use the Download TrekBuddy Atlas Creator 1.6.1 - Design atlases with this tool. - Softpedia
Trekbuddy Atlas Generator.
you can copy the map files onto your SD Card, and use them even when you're out of coverage area. I do this all the time, works great.
The map data can take space, but I generally use a max of zoom level 12, and a city level map (enough to navigate) of New Delhi takes up about 50 MB, so it's not that. Of course, if you want to carry around a detailed map of a very large area, things will be different, but I think what you want is the ability to navigate when you don't have data access, and this lets you do that.
If you need more help, let me know