Something like this app on a phone would only update via your phone network's cell tower wouldn't it?
This was my thought until Gavo went to NR this year, his updated every 20 or so minutes across the paddock.
Alan, I believe you are correct, it will store the gps points in the phone until it locks in with your phone network cell tower. This then will update all the points since its last connection with a cell tower. Bubbler needs a wifi/wireless and/or a cell connection (depending on how you set the settings), to transmitt its points.
Obvious choice for service provider is Telstra due to monopoly of cell towers around Oz. I can remember being somewhere out your way Alan trying to make a call on my mobile phone (Optus), coun not get a connection. A guy standing a few meters away was chatting away on his cell. He was with Telstra

so changed my service provider once I got back from my ride. If you are riding in high population areas then it may not matter who you are with.
Yorkie, I am not sure what the distance separation is for the towers across the paddock but I know on some of my trips I actually lost cell reception for some periods of time. Bubbler just "caught up " with the gps points and updated Spotwalla as if it was constantly updating?
Bubbler Pro is a good bit of kit for my Android phone
