I used Stub Hub when I went to the Rogers Center in July. I read that I am able to use the bar codes on my cell, however I was nervous and with my family so I had the Concierge at my hotel print them out. Turned out I would have been fine with my cell. The only issue is if your cell freezes, battery dies, you drop it etc, you are screwed.. So my advice is if it is not a PITA to print them, print them. If it is, then just go with your cell, but make sure you have a full battery and don't drop it')
Edit to add, I know my example was Rogers center, but Yankee stadium does accept mobile bar codes from Stubhub. Other sites they might not, Stub Hub they do.