I picked up a subsidized 6 in Jan and am locked to my two year plan (to apple's credit the replaced the phone for a clicking screen - no questions asked), but my wife is looking at a 6s and I was surprised to see that she has to buy it outright or get into some kind of lease or payment plan.
Much to research I guess.
The way around that was to buy a phone outright from the manufacturer/Amazon which is how I made sure my unlimited plan stayed unlimited. The last new phone I got when I was on AT&T was a blackberry bold
I have both, and TBH I mainly read of the iPad (using the Kindle app). The iPad is more versatile and I can use it to listen to music etc at the same time. The only time when the kindle gets preference is on holiday when I am reading outside as the ipad doesn't handle glare very well.
I very rarely buy a paper book theses days except for art related ones