Disconnected (1984)

Lovely young Alicia starts receiving bizarre and disturbing phone calls after breaking up with her boyfriend Mike who she suspects is cheating on her with her twin sister Barbara Ann. Alicia meets and befriends amiable, but awkward film nerd Franklin, who alas turns out to be a total psycho with a penchant for carving up nubile ladies. But is Franklin the nutter responsible for those distressing phone calls?