We used the navfree App downloaded to my phone for sat nav when we were over there a couple of years ago and it worked great. It downloads the maps to your phone so that you can use it offline. It does require a bit of space on your phone though.
You need to have internet access to use the search function for addresses, I preloaded and saved addresses for anywhere we thought we might visit on our trip before we left. Once the address is saved it will navigate to it offline. We were driving around and staying in motels though so tended to have wifi in the evening if we needed to add any new locations for the following day.
Also used a paper map and the search on map function when needed to key in a destination or Starbucks free wifi.
