> Is it important? It uses two capacitors as AC filter and then a diode bridge
> also to stabilize the signals.
>
> Actually I'm very new to electronics.
> If you think the problem is isolation from telephone line would you please
> explain me why?

I highly recommend that you get a copy of the book "understanding
telephone electronics".

Properly designed isolation from the phone line is critical to
anything like this working properly, and also not disturbing the telco
network, or endangering phone technicians.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist