I got a phone call too, about 2 to 3 weeks ago. It was from the 800 number and not from Singapore, but it was to tell me I was upgraded (I had applied an RUC).

Truth be told, I thought it was weird.

When your cell phone rings on the same day of travel and the display reads "Delta", my first thought is that it's the automated system telling me that my flight was cancelled.

Personally, the standard email that "your upgrade has cleared" would have been sufficient. And it's a lot easier to choose a seat yourself online when you can see the configuration and what's available. It take more time to have the phone agent relay that to you and for you to process that info and make a decision. (I ended up just taking a seat over the phone and then switching it online).

Sorry to appear ungrateful, but I didn't love this change.