Another + of the apps is that when you're not in coverage areas, the app continues to collect data and then updates spotwalla when you get back in range. That's nice for reviewing and sharing trips and such. But. *Still, hard to beat the awesomeness and robust safety that comes with satellite (SPOT) tracking. Also, to my knowledge, the rallies that require spotwalla (ie: IBR, cognoscente, Big Sky etc etc) they all require SPOT and not apps.
BMR next year might introduce some techy spotwalla functionality ...and either apps or SPOT will be acceptable.