Using an external VoIP product

My employer has a phone system for all remote employees called Communicator which uses a softphone VoIP feature for outgoing and incoming calls using a number based at their HQ.  My Outgoing voice signal is illegible buzzing sounds and other noises.  I have the Hughes voice service but as far as I can tell, the only calling I can do is by plugging a traditional phone into ATA jack. Is this the only way to utilize the voice service or am I missing a simple concept or installation procedure?