To masturbate with every intention of ejaculating as quickly as possible. It's used to describe the masturbater on the go, one who can't take his time and is in a hurry. The phrase is a reference to the Stargate MGM TV shows that have numerous scenes of people "dialing" to activate the gate portal into another planet. Often there is an ancient dialing device or a human computer one. The popularity of the phrase remains relegated to stargate fans or sci-fi nerds in general because no one else is likely to understand the reference.
I caught this guy in the park dialing the gate like it's no body's business.