How to know if someone hacked into my iPhone?

I've heard that it's not so hard to do. I'm sort of worried. Is there any where to find out? Also, I asked one of my suspects online if they did hack my device or not and all they said was that they don't even know how to open their iPad or utilize their Black berry and then I asked if he knows anyone who did hack and he said yes and it was a friend and I asked what was the device and he said Black berry. I'm still worried that someone hacked into my iPhone. I've heard celebrities who tap into their husbands or boyfriendd phones to find out information and they make it sound so easy. I'm worried and I need a helpful answer.

Can I move my kindle books over to my iPhone?

I already have the kindle app and everything, but I just don't like the setup as much as I do the iBooks setup. Is there someway to download the book to my iPhone without having to purchase it again?

IPhone 4S volume down button stuck?

I've had an iPhone 4S for around a year now or about that and a few months ago (I can't remember exactly when) my volume down button randomly stopped working.
As far as I can remember I hadn't dropped it or any thing like that.
If I move it from side to side and up an down with my nails it moves fine but it's just when I press down on it it feels like it's stuck in.
The volume up button works perfectly.
It's been stuck for awhile and I've been using the control centre to turn the volume down but now I'm just sick of it.
Anyone got any solutions?

My iPhones vibration is not as strong?

So I dropped my iphone on concrete today from about shoulder height and it landed screen down, it didn't crack which is suprising! But the vibration doesn't seem to be as strong, what could I have damaged to make it do this?