We highly recommend having a fully functioning phone while abroad. Relying solely on WiFi is typically not sufficient. Check with you phone service provider about international plans, or use a local SIM card. To use a local SIM card, your phone must be unlocked. If your phone is paid off, you can ask your phone service provider for the unlock code. Make sure you do this before you go abroad.
Here are some comments from the previous students regarding the phone:
I bought a SIM card with a reloadable data plan from Telekom (German division of T-Mobile) for 15 EUR per month. There are probably cheaper options, but this was convenient and had good service throughout Europe. I recommend keeping your current phone and buying a SIM card for it anywhere in Europe because there are no roaming fees in the EU.
I used sprint which had international data and calling.