While I would still recomend running all three, Gizmo has made a pretty incredible offer that we should all try out:
If you download, install, and use GizmoProject - you will be able to make calls to another user's computer, mobile or landline for free!! I have installed it and have followed the instructions. Now I await others to do the same.
Note the fine print:
Callers are encouraged to make free PC-to-PC calls whenever possible. The All Calls Free calling plan applies when both call participants are active Gizmo Project users making a few phone calls per week with Gizmo Project. Free calls may originate from anywhere in the world, but must be to a qualifying number in one of the 60 countries for which the plan is offered. Calls must be made from the caller's contact list to either the "home phone" or "mobile phone" number the call recipient included in his or her profile, and both parties must have shared each others profiles with one another. If a call does not quality as free under the All Calls Free plan, it will be subject to our regular low calling rates. As with all of our services, the All Calls Free plan is subject to the Gizmo Project terms and conditions and end-user license agreement. More information, including the qualifying country list, may be found in the All Calls Free FAQ.
Something worth remembering about Gizmo is that it also offers free conference calling and audio recording, as well as a fun intergration with Google Maps.
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