SIP Phone Clarity

I am using a SIP (SESSION INITIATION PROTOCOL) phone at home that connects through the net from NC to MA. Then it connects into the Mitel PBX switch at that building. Most of the time, it is choppy and me the the person on the other end can not understnad one another. I am on TimeWarner cable at 5M up.
Is there anything I can do on my end to improve on the clarity? I have nothing hogging the net resourses (I am not downloading or uploading anything.)
Thanks.