Cell phones are a good idea, but it is certainly not something that you must have. Some programs do provide cellphones, or will offer cell phones at a discounted rate. You can easily rent or buy a phone while you are abroad. They do not use contracts in the same way we do. You will buy or rent a phone, and then purchase a SIM card you will "top off" when it runs out of money. This is an easy pay as you go alternative to signing a contract. Many plans include free incoming calls from anywhere in the world if you do buy a cell phone. This option is usually the most cost-effective for long-term programs; former students and/or the program provider can provide details as to the best local stores and service plans.
You can take your U.S. phone abroad with you. You should verify with your cell phone service provider that your phone will work in your program location. However, using a U.S. cell phone with a U.S. SIM card is usually very expensive, even if you are able to purchase an international plan that reduces the calling rates. If your U.S. phone is unlocked, you may be able to purchase a local SIM card in your host country and use it in your phone while in the host country.
If you decide not to get a cell phone, there are calling cards and pay phones everywhere for you to use. Regular calling cards tend to be more expensive, but prepaid calling cards get you more in minutes and allow you to add minutes as you need them. You can find prepaid calling cards in the U.S. and abroad.
Students also often use apps such as Facebook, Skype, FaceTime, Viber, Whatsapp, Textme, and personal blogs as a way to stay in touch with friends and family back home.