I was a phone phreak, and I still have my last old-school brown Radio Shack tone dialer which I’d been planning to make into a red box. Ultimately I was too lazy to swap the crystal in it, and it sat in my junk drawer for years while red boxing died. Now it’s a curiosity that sits on my shelf of hacker books. Maybe I’ll still do the crystal swap someday for the sheer hell of it.
There is indeed an app for Android!