Can i put my sim card into the iphone 4?

I have a ATT phone without a data plan, and someone is offering to sell me their iphone 4. My friend told me if i jailbreak that iphone it would work, i could text and call and stuff, just not be able to connect to internet

Yes, you can put your Sim Card inside the iPhone 4, considering if it is unlocked.

Unlocked means the phone can be used with unlimited sim cards, and is not restricted to certain sim cards. Locked means the phone is restricted to one carrier (one sim card).

Unlocking your iPhone 4 depends on what operating system your running. If you do that, you can unlock your device. You DO NOT need to jailbreak it in order to unlock it.

If you would like to unlock your iPhone 4, go to this page: http://www.iclarified.com/unlock/. Choose your device (iPhone 4) and select what baseband you have and iClarified will guide you through it. If you do not know how to find your baseband, go here: http://www.iclarified.com/entry/index.php?enid=2543.

Also, if you unlock your iPhone, you will still be able to connect to the internet.