VOIP Problems

All of a sudden the VOIP phone on my wife's VPN stop working and we were unable to connect to the server in the main office in her Atlanta based company.  They have been unable to determine the problem.  I was attempting to work out of the house last week on a different VPN and discovered my VOIP was not working also.  All other internet functions are fine on both networks.  Bought a new modem over the weekend and now there is no connection at all for her phone and mine still will not connect.  Could it be the router?  I really need help on fixing this.