1)  Call someone with your speakerphone.  

(Make sure they are not on a cell phone as almost all cell phones deliver poor
conversation quality and it would not be a fair test of your speakerphone.)

2)  Have the person you call start counting or just talk continuously.  At the same
time they are counting, you say the ABC's or just talk continuously.  

3)  Did the person hear all that you said?  Did you hear all that they said? If not,
then you have just experienced poor conversation quality.
CONVERSATION QUALITY TEST
SP Communications
Creators of the Tru-Talk Personal Speakerphone