Two notes:
1- WAZE DOES use data! That is a streaming mapset and when you lose cell signal, you lose WAZE.
2- There are several REAL GPS apps for Smartphones that work exactly the same as a standalone GPS, and they will not lose their map data or position when either going to another app, talking on the phone or loss of cell service. For the iPhone I use Navagon. They also make stand-alone GPS, but they pulled them out of the US because of competition with Tom-Tom and Garmin. Navagon has since been bought by Garmin about 4 years ago.