If you travel to Ukraine you will want a cell phone to use while you are there. You can purchase any unlocked tri or quad band phone that uses sim cards from ebay. If you already have a phone from places like T-mobile or AT&T all you need to do is unlock it. Sim card is a small card that allows you to have a local number when you travel. The newer I phones such as the 4 use a smaller version so unless you want to do some adjustments I do not recommend using it. MTC is one of the local cell phone providers for Ukraine but you might want to ask your friends what provider they use so calls will be quite inexpensive.
You have a few options, you can purchase a phone when you land for around 200 dollars or buy one from ebay starting at around 65 dollars. You have to decide what options are right for you since some even come with dual sim cards and a lot of memory. If you already have a phone you can use such as the I phone 3gs all you need to do is unlock it.
Me and my family have the Samsung Infuse 7 dollars to unlock online, A phone from china called an I64 around 65 dollars comes unlocked and an I phone 3gs I paid 15 dollars to unlock. All these phones can be purchased online for use in Ukraine from online retailers. Make sure when you purchase your phone that it is unlocked saving you a few dollars. Now that you have your phone all you need to do is purchase a sim card at the airport or in any city in Ukraine.