Is it proper to call my ex to inform him that I'm engaged?
The only time you should definitely spill the beans about your engagement is when you have kids with your ex, as your new marriage will then strongly impact his or her life and the lives of your children. If you're still friendly with your ex (or at least civil) and you run into each other or chat sometimes, it's a nice thing to let him or her know -- everyone likes to know when their former lovers have moved on. But if it's someone you never see anymore and really don't care to see, you don't need to track him or her down to announce the happy news.
Popping the Question