It seems like airlines all around the world are racing to allow passengers to check in for flights using only a mobile phone. Delta Mobile Check-In JokeI wrote about Air Canada rolling it out last year, and lately both Continental and Delta have put out tests of their own. Delta just put out a blog post on their test as well. It sounds great in theory, but you might want to think twice about it if earning miles is really important to you.

Fellow airline geek and aviation consultant Roy Rosales brought up a good point in an email yesterday. If for some reason miles don’t get credited to your account, you usually have to send in your boarding pass for credit. If you use your cell phone . . . there is no paper boarding pass to send.

In Roy’s case, he flew on a Hawaiian Airlines flight and expected to get Continental miles. They never showed up, and he called Continental to see what happened. Roy was told that an original boarding pass was required in order to get credit. He was curious so he asked what would happen if he had checked-in online and the airline kept the boarding pass, as some do. The agent said it didn’t matter – no pass, no credit.

So, until the airlines decide to somehow alter those policies and email you a PDF that can be used for redemption, you might want to consider keeping a paper record, especially if you’re flying on one airline and trying to earn miles on another.