David Robinson of Stack Overflow lays out the evidence in a blog post, analyzing roughly 1,400 tweets. He shows that Trump's (real) Android tweets are mainly sent in the morning, while those coming from an iPhone are sent in the afternoon and early evening. Also, Trump's habit of manually retweeting others (copying and pasting their tweet and surrounding it with quote marks) happens nearly exclusively in tweets sent from Android, while tweets sent via iPhone were 38 times more likely to contain either a picture or a link. Robinson points out that this makes sense, as these tweets tend to be announcements of one sort or another — exactly the sort of administrative message that campaign staff would need to publicize. Compare this, from an iPhone:

To this, from Android:

Robinson also uses sentiment analysis to compare the types of words used by Trump's Android-tweets and iPhone-tweets. The result? "Trump’s Android account uses about 40 to 80 percent more words related to disgust, sadness, fear, anger, and other 'negative' sentiments than the iPhone account does," writes Robinson, adding that "the positive emotions weren’t different to a statistically significant extent."

You can see that difference in Robinson's charts below:

So, what do we learn from this? First, it seems pretty clear that Trump's Android tweets are written by the man himself, while those from an iPhone are more likely to be the work of some poor staffer doing damage control. (Although the iPhone tweets do sometimes replicate Trump's way of speaking.) And second, that creating an atmosphere of fear, anger, distrust, and suspicion isn't just an electoral strategy for Trump — it's also part of his character.