I sent an e-mail, expecting a bad response. On a Monday. With less than a week to go until I went full time. The next day I got an e-mail back that started with "Hi Paige!" from my mom. There was a little wobbliness in the beginning but we got through it easily enough. Mind you, of my parents she's the Religious Conservative. My dad is the Atheist Liberal and he's the one that's barely talked to me since going full time. Everyone is an individual so knowing how they're going to take the news is a tough thing.
I do just always recommend accentuating the positive. The healing, the happiness, the relief in your life. That kind of stuff. Helps make the moment the "good time". More like "I won the lottery!" instead of "I wrecked my car!" as the former is a celebration and the listener can assume that you're ok, the latter is stress and the listener could be worried about you.
Best of luck!