Ah, great ideas, Faterson. This isn't an option for me right now, but maybe when DH and I are in the U.S. more, we'll find it worthwhile to purchase unlocked phones and get SIM cards to use there.
As for keeping a large library on the iPad mini, I do want all my books on mine. I don't know how many I have, I've never actually counted, since they're spread across different formats and readers. I just like not being dependent on an internet connection to choose what I decide to read in any given moment.
I do have the files on a PC and in the cloud as well. I guess we each do what works for us and according to our preferences.
This thread has provided some great ideas for handling ebook libraries and files.