Totally reliable if your computer network is ready for it.  It may need to be reconfigured or upgraded to become VoIP-ready.   Your ISP needs to be set up to provide high quality VoIP.  Their system gives voice data priority over other data and for some companies this may mean changing your ISP.  If you have more than one office, use the same broadband provider for all.  VoIP performance is enhanced when calls travel over a single provider’s backbone.