Your suspicions are well-founded. According to recent research on the topic, more than 60 percent of conference-call participants are multitasking, including emailing and texting. About half of the people on the conference call are eating, and one in five is shopping. So, multitasking may be commonplace, but since you can't see what others are doing when they are out of your sight, you'll need to establish a four-step strategy to offset that disadvantage.

First, always consider whether the conference call is necessary, or if the information could be relayed some other way. This might alleviate some calls, and thus sidestep the problem.

Second, for those calls you must make, establish some ground rules beforehand. Send emails asking participants to turn off their cellphones and other nonessential devices. When the meeting begins, reinforce the email's message by again asking everyone to shut down their devices.

Third, during the call, periodically ask questions of participants to essentially force them to pay attention. If possible, delegate parts of the meeting to participants on the call so they will have to contribute, and have less time to focus elsewhere. Last, plan a short break in the meeting to give them a moment to check their phones, email, etc. If you try these steps, their heads should be more in the game, and less on Facebook.