well, yes its illegal as far as i know, however i already own one which i purchased 5 years ago, its cheap, costs around 500 Q.R
there are two types, one that should be connected with normal UTP cables and second should be connected to the telefon (RJ11) connector dial up connection, I have the old one which is dial up.
each device has two ports, one port should be connected to the router device and the other to a phone handled.
if u r interested to have the old ATA u can take mine for free...or else i can lead u to the best website that can deliver it to ur house with an excellent customer support services