What will the experience be on my Nokia device when I am transitioning from 3G to 2G and vice versa?

Going from 2G to 3G and vice versa, is a seemless transition. All data applications will still function. You may encounter slower data transfer speeds when in 2G mode. Ovi Maps will not be affected. The built-in GPS can be used even in offline mode when the map data has been pre-downloaded to your device memory.