That's quite true. Eventually, it will show up. I was using Bubbler GPS to Spotwalla in a 12 hour rally. About half of my OK messages required at bonus locations for live scoring, did not show up until the following day. Thankfully, that rally live scored me when I got to the finish w/o penalty. It was, however, more work for them. If I had just kept my Spot, I would have had no issue with live scoring. My data plan simply couldn't handle the OK on top of bonus pictures being sent and throttled me down on data. Now, I will never know if the pics would have made it through w/o the OK pings, as the pics are more data heavy than the pings.While it's definitely true you can run into areas of the US when your cellphone loses its data connection, that doesn't mean that your track won't appear on Spotwalla. The app (BubblerGPS on Android) on your device still reads GPS info from your device regardless of a cell data connection. When that connection is reestablished, all stored data is sent up to Spotwalla's servers.
The lesson there is to know what your cellular data plan will do if you exceed certain levels in a short time period.