Customers with VoIP services such as Vonage, Comcast, etc, experience this issue with their call blockers blocking call the incoming calls (applicable to V5 or V6 models).  Below are some solutions:

1) Change your modem -- If you have an VoIP service, chances are that the signals on your modem are not optimum (e.g. higher current levels than needed).  For example, Vonage router/modem model HT802 exhibits higher currents level on the LINE port.

2) Use 1k Ohm Patch cord -- If you are unable to change your modem, you may build a special patch cord using two (2) 1,000 Ohm resistors on the tip & ring (Red & Green wires).  If you need help with this, please contact us.