Can I bring my iPhone to Germany?

I have an iPhone 4 with AT&T. I will be going to Germany for a month and I would like to bring my phone with me so I can text my best friend and family while I'm there. My dad said it would run data up, but I think you can turn it off somehow to where it only operates with Wi-Fi. I would like to tweet and post on Instagram if I'm there.
I don't know what I can do. Any help would be appreciated.

Yeah just go to Settings > Cellular and turn it off.

Hope you have fun in Germany! Auf Wiedersehen!

What you can do is keep it on airplane mode. You can still turn Wi-Fi on, even though it turns it off automatically. Not only will this save battery, but it will make sure that you can't connect to a cellular network and no roaming charges will be added. TURNING OFF 'CELLULAR' IS NOT ENOUGH! All this does is turn off the 3G (or 4G, or 2G) connection, without turning off the rest of the network connection.

Again, after you switch into airplane mode, just turn Wi-Fi on and connect to a network.

Have fun in Germany!