I have used the Navionics Web App, and I love it.  Is the phone app like having a GPS on a sonar unit.  It is hard to ask what I am think but is it like the web at where you can scroll anywhere or can you do that but it also shows you where you are.  That is what I want, for it to show me where I am and mark waypoints.  Also there are so many versions ranging in price, which one should I get?

Nice site.

Yes, the Navionics Mobile App works like the Navionics software used with sonar/GPS units and has the same detaill as the Web App.

You have to turn on your device's GPS for it to show where you are.

 

You can get both the Nautical Charts and Sonar Charts with the mobile version HD.

 

You download a free trial version called Navionics Boating. Refer to their web site under the Mobile tab.

The app is worth purchasing if you do not have a GPS unit on your boat. I have a holder for my phone on the console next to the sonar and just use navionics android app. Works fantastic. If you want to keep it running you'll need to wire in a 12V electronics port and then use a cig lighter adapter to keep your phone plugged in. The app drains phones fast. 

Also to add to the subject, I was at Icast this year and they are in the works to making the Vexilar WIFI sonar the ability to link into the app so you can also view a fish finder and overlay depth on the mobile apps.  Its a pretty sweet deal.