I have moved your post to a new thread, so you can get help from the community.
Help from the moderators is by invite only.
Usually VOIP will work or not, intermittent issues could be down to your broadband connection.
As you have a HH5, please can you go to hub manager then troubleshooting then helpdesk and post lines 1-12
That will give forum members some idea of line performance.
Its also important that your computer is connected using a direct Ethernet cable, and not wireless, as wireless is likely to give you lots of problems.