just look at this thread: Replacement for Google Maps? - it’s a good example for what i mean: people talk about gui (…using qt…) when talking about map provider. i see a map provider as a service in the phone which has no gui at all but provides maps via api for a potential gui. so you can choose both ends: decide to use google maps and qt or osm and whatever or anything else.
on a phone it’s vital to separate things correctly.