They discovered that:
"The intervention group showed significant improvements in functional capacity relative to the control group (15% net VO2max increase in men, 9% in women), high exercise adherence rates (90% for men, 75% for women), and 1.5-kg body weight decreases in men."
The researchers chose telephone counseling instead of face-to-face contact because it has most of the same benefits without similar drawbacks (time consuming, need to be in the same geographical location). They also saw it as a good alternative to the social motivational benefits of gym classes, when people are only able or willing to exercise at home.
This shorter study was followed by the "Stanford/Sunnyvale Health Improvement Project I" which ran for 2 years and concluded that:
You can find an abstract here and the full text here.
What could this mean for you?
If you rarely muster the motivation to go the gym, can you ask a friend to give you a ring on an appointed day? They can check up on how you've been doing that week, or encourage you to go to that class after work.
Perhaps your motivation is rock-solid, but you've got a friend or relative who could use some encouragement. Next time they moan that they "always forget to exercise", why not offer to give them a call as a gentle reminder?