We are traveling to Switzerland and Italy in June. I have gathered from the discussions on this site that it's best to buy point-to-point in Italy and the Swiss pass for Switzerland instead of the Eurail pass. How does it work when we cross the border from Interlaken, Switzerland into Italy?
At the train stations in Interlaken Ost or Interlaken West, buy your ticket to your destination in Italy. You should only be charged for the portion that your Swiss Pass may not cover plus the Italy portion. It will be a complete cost. Once in Italy, you can buy tickets to other destinations. Works the opposite as well. For example, purchase a ticket in Venice to go to Interlaken Ost and you will buy the entire journey at that time. The countries work very well together in that regard.