Continuity mistake: When EB is young and is in the factory for the first time, he picks up some sweets off the factory line. The amount of sweets in his hand then changes between shots.
Revealing mistake: When E.B. Is drumming along to Dynamite at the "Hoff Knows Talent" audition there is an audible bass drum beat but via several overhead shots you can see that E.B.'s feet do not reach either the bass drum or hi-hat pedals.
Continuity mistake: When the car in which EB is a passenger pulls up at the mall and parks, the window in EB's door is completely raised. Then the driver gets out and the window is a couple of inches down from the top. Then EB climbs out of the window - without winding it down - and the window is now about six inches down in the door.
Other mistake: When EB is playing Rock Band, the TV shows the drum playing rapidly, but EB is playing the same beat he was before the solo.
Revealing mistake: When E.B. is running by the Hollywood sign and we see his shadow on the sign, at one point the shadow doesn't touch the ground when it should. It hovers.
Visible crew/equipment: When James Marsden arrives at the house he is watching, he hurriedly opens the door and the camera pushes in on him. The reflection of a crew member can be seen in the left window. It's clear enough you can see the person turn their head.
Answer: Phone.