On the OneNote for iOS front, here's Microsoft guidance for users of the current OneNote for iPad app:
"If you are an iPad user today, you will need to get the new OneNote app from the store. When you open your current iPad app, you will see instructions for getting the app. If you are an iPhone user, you don't need to do anything--we merged the iPad app into the iPhone app so you already have it."
The new universal OneNote app for iOS includes a number of updates for the iPhone version that are now available for the iPad, too.The OneNote app for Android is already universal, meaning it works on both phones and tablets.