|^^^^^An ATA (Analog Telephone Adapter) box is intended to connect standard telephones to a non-standard telephone system such as VoIP and is sold along with the service itself. The OP never mentioned he had VoIP service or telephone service of any kind. In fact, he corrected himself by saying:|
I mean a land line, ok not a land line, but an intercom, where it can only call within my house, and can't call outside
Based on his post, one would have to assume he only had an internal intercom system which he would like to use for international calls through his computer ... which, in itself is impossible. In using an ATA box, he must already subscribe to a VoIP provider ... again, something he never said he had.
Other posters simply recommended the alternative ... for him and his chat buddies to sign up for the same IM service and talk computer to computer for free. Nothing difficult about that.