Why did she get another silent call at the end.
It was a silent call for those who think she was chatting to someone.
Because when ever she got a silent call we the viewers, were able to hear the silence or what was being said in the call.
When Klute was in her apartment for the first time she had a silent call and pretended to talk to the silent caller, to show Klute that there was nothing wrong in her life.
At the end of the film she got another silent call and again pretended to talk to the silence.
The killer was dead, why the silent call? Maybe she got lots of silent calls. it's New York.