Seeking kiddie anthology with telephone monsters, 13-year-old boy with telekinesis

When I was a young kid (I'd guess abound 6-7 years old) back around the late 70's, I read an anthology of fantasy, or of fantastic stories at any rate, that really made an impression on me and still pops into my head from time to time. I'd like to read it again, but I only recall the basic plots of two of the stories. Help identifying the book would be most welcome.

In one of the stories, a child is at home alone. He takes the phone off the hook and hears the dial tone. Eventually the dial tone grows louder and louder, until a monster who somehow embodies the tone (?) emerges and menaces him. Later the sound coming from the phone changes to an off-hook tone, and a second monster emerges to save the boy from the first monster; both monsters return to the phone. It sounds silly as hell, but at my tender age, the sounds that come from my family's phone were pretty mysterious, and I found this story genuinely unsettling.

The other story--the final, and also longest, story in the book, by my hazy recollection--was about a boy who was born on Halloween, and a weird adventure he had on his 13th birthday. He discovers he has telekinesis (or maybe already had known this previously), is kidnapped by government agents, and imprisoned in a facility beneath a mountain. He decides to test the limits of his power, causes an earthquake, easily breaks the locked door of his cell, and floats to freedom by using his T.K. on himself (a concept that kind of blew my young little mind).

This was a really long time ago, so caveats about unreliable memory apply. Conceivably the stories are not from the same anthology at all, but that's how I've always remembered them.