I just talked with OnStar a few days ago about a internet issue, and, they also told me I should use MyChevrolet and not OnStar app. YMMV
As I have an iPad, what he says is true, it's an iPhone app, but runs on the iPad, just portrait.You guys with the iPads might have to choose some different options when searching the app store. An iPad defaults to search for iPad specific apps. The MyChevrolet app is most likely designed as an iPhone app, not an iPad app. It will run and work fine once you find it, but it won't just show up without changing your search options to include iPhone apps. I've had this happen with several different apps I wanted to add to my iPad
Stupid, I know, but give it a look.....I'll bet its there.