Phones and the cloud - what goes into the cloud from/to our phones?

[BinaryBit]

1. There's texts, videos, images being uploaded and downloaded through the cell-phone network, but where is it all stored when it is moving? Is it stored in the cloud and can anyone access it even though it might be encrypted?

2. Where are e-books (.mobi files etc.) actually located when I buy one from say, Amazon. Are they on my phone or Kindle or tablet or located somewhere else (the cloud?)?