if you do not want to install GizmoProject's client, you can use other generic VOIP Client too. e.g. X-Lite.
Here are the settings verbatim from them:
SIP account InformationDisplay Name: (Display name that you may like to use - say Gizmo - your name)
User Name: (found in your Gizmo Project profile)
Password: (exactly as typed in Gizmo Project)
Authorization User Name: (found in your Gizmo Project profile)
SIP Domain: proxy01.sipphone.com
For Domain Proxy, you can select options as defined on the screen right now.
SIP Address: 220.127.116.11
At this time, SIP Domain and SIP Address reflect same server.