There are a number of reasons why a message might not get across properly. Perhaps the speaker is not being clear enough or the listener is not really paying attention. Maybe there are cultural or technological issues at play.
Regardless of the culprit, when information isn't correctly transmitted from the speaker to the listener, there is no effective communication happening and everyone's time is wasted. In addition, misunderstandings or miscommunications can cause a number of problems in both interpersonal and business relationships.

Physical Impairments to Communication
While modern life has made great advances for the integration of those with disabilities, these folks do still face many challenges in daily life. Physical impediments can definitely interfere with a person's ability to communicate, whether that means having trouble getting an idea across or struggling to hear or understand a response.
One such impediment is a speech disorder. In fact, these are sometimes referred to as "communication disorders." Someone with a speech disorder may lisp or stutter. Others may not have the ability to speak at all. Likewise, a hearing individual and a deaf individual may experience some difficulties in communicating effectively.
While much of the responsibility for dealing with these situations falls to the person with the impairment, the other people in the conversation need to do their parts to ensure that effective communication is happening. This may involve simply asking the other individual if any accommodations would be helpful. It also involves being respectful when asking for clarification on things that may not have been understood.
For example, an individual with cerebral palsy might have no problem following the conversation and formulating intelligent responses. There may be difficulty, however, in articulating those ideas. The others in the conversation should remain patient and respectful and avoid being patronizing or brusque.