If you take a GSM mobile phone from your home, just note that prices of cellular phone call are VERY high in Ukraine. Please check at home with your GSM company about the rates in Ukraine. I know that 1 minute call can be about 5$.....
Crossing the border from Romania.
If you come from Romania, and you listen to my advices, please arrange the border cross with Zoya. At the border, the old Comounist way of thinking is ruling.
Don't joke there with the soldiers, don't laugh at the front of the soldiers while talking in your language.
Please note that the Visa you get to Ukraine (depends on your origin country if you need Visa) costs about 140$ for one month.