If I buy an iphone 4 can I take the sim card out of my old phone and put it in?

If my phone is unlocked and I put a sim card from my old phone into the new phone do I still have to pay for internet

You'd need to either cut the sim into a micro sim or order one from your network provider. The iPhone 4 and later models all require a micro sim to work

Unfortunatley you have to call your service provider (Sometimes) to let them know you are using an iPhone because iPhone/ Android has there own data package. Sometimes it will work. Try it and see if not you have the other option listed first! Goodluck!

You don't put SIM cards into iPhones. And if you ave Internet at your house like Wi-Fi etc or you know of a location that offers free Internet, you simply connect to it. No card needed

Nope! Unless You Had An IPhone Before. IPhones need a special sim called a micro sim! And Smartphones have to have a data plan! If you didn't why would you even get a smartphone! Sorry