Love Mobile Passport. We have used it in several airports coming back into the US. On a recent trip coming back from Europe into JFK, I was the only person at the Mobile Passport Immigration officer's station. I was through in less than a minute. The regular line was very very long and not moving terribly quickly. Not all re-entry airports have it and sometimes the signage is a bit of a mystery but employees have been able to point us in the right direction. As Beachnut82 said, we have not always been able to transmit on planes' wifi and have had to wait until we have cell service or airport wifi to submit.