How to stop my iPhone doing this?

OK, so I've recently gotten an iPhone 4, and whenever my sister texts someone like my dad or my mum or whatever, the texts come up on my phone. How do I stop this happening?

Go into settings and check what apple ID is on there. It's probably got your sisters account listed, remove it and the texts (iMessages) should stop coming in.

That happens if your using the same apple account. Make one for yourself and change it in your phone settings.