The first cartoon to feature Mickey Mouse speaking in his familiar falsetto voice (two previous cartoons, "The Karnival Kid" and "Mickey's Follies" had him speaking at a comparably lower pitch).
A Mickey Mouse and Minnie Mouse toy, that was inspired by the 1929 Cartoon "Mickey's Choo-Choo" was sold by Lionel and saved the company from bankruptcy. That is why Mickey is also known as "the mouse that saved Lionel".
"Mickey's Choo-Choo" from 1929 is Walt Disney's first time voicing Mickey Mouse in his iconic higher pitched voice, and also the first time, in which he says actual phrases in the higher pitched tone.