With WP 7.5 on Nokia Lumia 920 I had voice directions that said things like "You've gone a different way." Now I'm on 8.0 and I don't have those any more. Maybe something else turned them off. How do I turn them back on?
I don't know which navigation app you used in your LG WP 7.5 phone, but you can have voice guidance with your Lumia 920 by using Here Drive.
In Here Drive, select Settings > Navigation voice, and choose the voice you want to use. If needed, press the "Download New" button to get other voices.
Some other instructions that may help you : http://here.com/help/wp8/drive/voice-guidance