IPod can see messages sent on iPhone?

My sister just got the iPod touch and she synced it on the family computer that all our other apple gadgets are on. She can now see all my iMessages I send and receive. How do I stop this? I don't want her reading my messages.

DOES MY IPHONE 4 HAVE A SIM CARD?

I have an iphone 4 (32GB - Black - Verizon servicer) and i want to sell it. I was asked if my phone had a sim card in it. I don't know the answer to this question. Does my iphone have a sim card? Also, if i want to sell it to a person who does not use verizon, what will i have to do to the phone?

I have an iPhone 5 16g do I need to back it up?

I keep getting messages to back up my phone. Any tips on how to do this? Also when done does it free up any memory? One more, does the camera have a zoom? The 3G did but I can't find it on 5.

What will happen if I plug my new iPhone into my computer?

I've had an iPod for a very long time and I have all of my music currently on my iTunes. I just recently bought an iPhone and I wanted to add some tones and various music to it. Will my music be okay if I plug my iPhone into my computer?

How to get back old default YouTube app on iPhone?

There are thousands of YouTube based apps in the App Store. I updated my iPhone over the weekend and my default YouTube app with all my saved videos are gone. How do I get them or just the app back?

I want an android phone like the iphone 5?

I have the iphone 4s and i like it but i'm ready to move on and have more choices. I want an andriod that has 4g LTE 4 inch screen at least and i would like a sd card slot
and needs to be 199 or under

Added (1). And i don't want the galaxy s3 its a little to big

Added (2). I'm with Verizon