We have Samsung Smartphones and one thing I've noticed when using the GPS (Google maps), is there is a dely. Often times we are past the intersection when it finally shows exactly where to turn. It's great for straight driving, but once in a town or city, the lag time is very frustrating. And if we are in an unknown new location for us (especially a larger city we are not familiar with), our Iphones are really just too slow. Our TomTom is right dead on, always ahead of time just right. We use TomTom because of this, but also, the GSP mapping on your Iphone or Smartphone will also eat into your data plan ... more than you realize. I suggest using both.
