To operate in Kosovo she will need a GSM phone that is capable of operation in the 900 and 1800 MHz bands. For Stateside operation it will also need to support 1900 MHz and 850 MHz (optional). There are quite a few on the market today. For a service provider, if she wants one from the States, she will need to talk to either T-Mobile or Cingular. I recommend contacting their customer service to see if either carrier has a roaming agreement with one of the Kosovo carriers. The carrier I am aware of is Vala900.
My suggestion would be to get a quad band (850/900/1800/1900 MHz) phone like the Motorola SLVR L7, RAZR V3 (or V3i), PEBL and others.
You can research phones here (http://www.phonescoop.com/phones/index_all.php). Be sure to use their phone finder (on the left side of the page). You will want an 850 MHz capable phone if you have to go with Cingular. It's optional for T-Mobile (they only operate 1900 MHz towers), but handy if you roam to anyone else while Stateside. You'll also want worldwide roaming. GPRS and EDGE are the two GSM data standards. Clicking another one like EV-DO will confuse things.
Tango Uniform