Non-OS ads allowed?

[Richard Gaskin]

I'm building my own ad server for a specialized desktop app, and it 
occurs to me that it would be useful to use those ads in mobile apps as 
well.

So the question is:  am I allowed to show my own ads in apps for iOS and 
Android?

I'm guessing the Apple answer is "no", but does anyone know if Google or 
Amazon prohibit the use of ads from outside of Google's system?

--
  Richard Gaskin
  Fourth World
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