Skype Dualphone 4088

I got the Skype Dualphone 4088 - connected it
with my optical fiber router and everything
seemed fine. No problems with Skype calls.
BTW - I am in Italy and naturally changed
these information on the phone.
Now I don't remember the initial configuration
if it was USA or GB.

However - I am unable to call out with landline.
I only can receive calls from landline.

I already talked to my phone provider (Vodafone)
and they told me that everything is fine with
the line....

I tried to connect my old Dualphone 3088 - but
it doesn't work with the 4088 base station.

Anyone an idea what could cause the 'defect' and
more important is there a solution for it?

Thanks already in advance.