Sonar charts using the SonarPhone T-Box....so i got this setup from Navionics to try out and never got a chance to put it on my other boat. If i understand it correctly i download the app on phone or tablet, go out on boat and record data and it will send it to the phone/tablet. My question is, do you have to have cell service for this to work? Also does this info get uploaded for sonar charts?? the places i fish are spotty at best for service. Looking to get it installed on this boat and give it a try.