Freeze the bowl to your ice cream maker ahead of time. (I keep mine in the freezer for whenever I want a frozen treat.)
In a bowl, stir greek yogurt, milk & sugar together.
Start your ice cream maker, & pour in yogurt mixture.
In a separate bowl, microwave frozen berries 30 seconds at a time until they are thawed enough to either puree or break up in the ice cream maker. (I did 30 seconds twice.) Then either puree the berries & add them to yogurt, or add them whole (they will still be pretty chunky, so if you don't like fruit chunks, puree them with a little milk or plain in a food processor/blender.)
Let mixture work in the ice cream maker for 10-15 minutes or until it balls up & is frozen. Scoop & serve immediately. Does not freeze well. (If you do freeze leftovers you'll want to gradually soften the mixture in the microwave 15 seconds at a time until you can mash up the mixture with your spoon.)