SC1200 and NETtalk Duo (VOIP)

[cscjjd]

Hi,

my SC1200 neither accepts incoming, nor makes outgoing, calls successfully when connected via NETtalk Duo (a VOIP device).
I tried adding a DSL filter and tried disconnecting the telephone from the Duo (and all other devices from the network router).
I have read one post which said the Duo did work OK for them.

p.s. It works perfectly when connected to a land line.

Any other suggestions on what to try with the Duo?

Thank you.