Dial H for Hero

Original Series and Silver Age
The series was a recurring feature in the anthology comic House of Mystery. Robert "Robby" Reed, a nerd from Littleville, Colorado (no relation to Smallville), found a dial with weird symbols on it. He translated the symbols (later revealed to be Interlanc, which I did a post on) into English letters and discovered that if he dial H-E-R-O would turn him into a superhero and  O-R-E-H would turn him back. However, other things could be dialed: minor thug Daffy Dagan became a super villain via dialing V-I-L-L-A-I-N and Robby's girlfriend, Suzzie, turned into a female superhero by dialing H-E-R-O-I-N-E. The dial's origin is unknown. However, the back of a Showcase Present trade paperback I own claimed the dial was from another dimension. One point after his series ended in House of Mystery, he helped the Justice League and let them use his dial thus turning them into other superheroes.
Christopher "Chris" King and Victoria "Vicki" Grant

Chris King and Vicki Grant found two dials (which only had the letters "H", "E", "R" and "O") in a haunted house and used them as superheroes to protect their town of Fairfax, New England. These heroes were based on submissions from fans. These dials could override the personalities of user (dialing H-E-R-O turned people into heroes regardless if they were good or evil). The transformations lasted for a single hour and the dials wouldn't work another for hour after use.
We discovered these dials were created by a person called the Wizard (unrelated to villain of the same), who was thought dead. The villains Chris and Vicki fought were lackeys for a mysterious criminal called the Master (a villain obsessed with the dials). The Wizard found the original dial and fused with Master into... Robby Reed! Apparently, Robby dialed S-P-I-L-T to deal with a dead man's switch. Dialing S-P-I-L-T caused him to separate into the Wizard (his good side) and the Master (his evil side). Robby gave his dial to Chris and Vicki's friend Nick.
After their series, Chris and Vicki gained the power to transform regardless if they had the dials. Vicki went insane and joined a cult. Vicki tried to kill Chris (who changed into heroes uncontrollably until he ran out of "energy"), but the Teen Titans saved Chris. Chris decided to use a special suit created by STAR Labs to control his powers and become a superhero again. Later, a guy named Hero Cruz found the dial and was attack by the still-insane Vicki. When Vicki used the dial, she regained her sanity.

H.E.R.O. issue 6

H.E.R.O. 
In 2003, the original dial got its own series: H.E.R.O. The series focused on the dial falling in the hands in various people, who usually end up screwing up their lives with it. A subplot was how an adult and bitter Robby Reed was trying to regain the dial as a serial killer tried to get it for own sinister purposes. The series ended with Robby and several people, who had the dials in previous issues, stopping the serial killer and internalizing the dial's power. The actual dial itself was sent to 50,000 BCE (issue 11 had a caveman finding it).
Dial H
In the New 52 universe, the overweight Nelson Jent found a phone booth that operates much like the dial did. He uses the booth to become a superhero An old woman, Roxie Hodder aka Manteau, also uses the booth.
References

• http://en.wikipedia.org/wiki/Dial_H_for_Hero
• http://en.wikipedia.org/wiki/H.E.R.O._(comics)