Because Inter-Tel was absorbed by Mitel, official downloads from the original "inter-tel.com" are no longer available. However, you can still find the utility on legacy software mirrors:

Double-click the installer to launch the wizard. Follow the on-screen prompts to accept the license agreement, choose your installation directory, and complete the installation. Step 4: Associate File Extensions

Ensure that the required ports for Inter-Tel Audio/Web conferencing are open on your firewall, or the player will not be able to connect to the server. Alternatives to Legacy Inter-Tel Collaboration