The VoIP press jumped all over “backdoor dialing” when Gizmo announced it. This is (or was) a catchy name for peering relationships that allowed Gizmo5 users to make free calls to a portion of US phone numbers. But there are problems in using the service in practice and the VoIP press and bloggers have not picked up on that side of the story with nearly as much gusto (read zero coverage).
There appears to be a “byzantine and shifting algorithm” that Gizmo uses to establish whether an account is permitted to use the backdoor service. These restrictions are not fully disclosed and accounts can switch between qualified and unqualified status without notice.
There doesn’t appear to be any way to tell whether your account is permitted to use “backdoor dialing” short of trying a call. You throw the dice as to whether the call will be charged or not. If you don’t have funds to pay for the call, in my experience, the destination “backdoor” phone number rings, and when answered, the call simply disconnects immediately.
Here’s what the Gizmo5 web site itself says about “backdoor dialing”:
Because these calls are bypassing the traditional phone network entirely there is no per minute fee or other charge…
If this is really true, then these calls should have no cost (or nearly zero cost) for Gizmo5, so why do they place these inscrutable restrictions on the use of the service? Was it just hype all along and really these “peering relationships” are paid terminations?
On the FAQ, under “Who can call a number with backdoor dialing?” it says:
Backdoor dialing is available for personal and business calling. There are no restrictions on who can call.
Gizmo5 claims that 11% of US numbers are reachable via “backdoor dialing”. In my research, I found that, in practice, I was getting more like 20% – 25% of the numbers I called could be reached free with “backdoor dialing” – that is, until it stopped working entirely about a month ago, as it did for many other Gizmo users.
