I would use the phone and credits to learn a new language and plan a surprise trip for my girlfriend. Her grandparents live overseas and don't speak any English and the last time they came to visit I had an almost impossible time communicating with them.
I'd use Rebtel to call international candidates for the job I recruit for. It's a significant cost for our business, a school, but with Rebtel we could significantly cut our costs!
I would use this to call my parents when they are outside the country. Would be great to get to talk to them more often! Good Luck all and have a great holiday.