Put the frozen fruit, yogurt and sugar in a food processor container along with a couple of tablespoons of water. Process until just pureed and creamy, stopping to scrape down the sides of the bowl as needed. If the fruit does not break down completely, add a little more water through the feed tube, a tablespoon or two at a time; be careful not to over-process or the sorbet will liquefy.
Serve immediately or freeze for later. (If serving later, allow 10 to 15 minutes for sorbet to soften at room temperature.).