Earlier quoted context omitted.
It was capturing telephone touch tones on a plate of glass. Olivia's smartphone could dial based on touch tones, that's totally sci fi these days.
Dialing back based on tones is not sci fi at all. The glass thing is sci fi though. Good stuff!
In the show, Olivia remembers those tones and happens to have an app for that on her smartphone, Walter doesn't make that leap.
I found some applications on the Play Store that can allegedly decode the tones, so it might not be so strange.