Harry Nilsson first met famed music producer Phil Spector at Perry Botkin's office in late 1964. "Phil was walking down the hallway and he heard my demo and he said, 'Who's that?' Turns out that Perry Botkin used to publish Phil when Phil was a teenager, and he said, 'That's Harry Nilsson.' Phil said, 'That's a good song. Did he write it?' Perry said, 'Yeah, well, he and I wrote it.'"
Harry and Phil wrote three songs together - "This Could Be The Night" (recorded by the Modern Folk Quartet), "Paradise" (recorded by the Ronettes and the Shangri Las), and "Here I Sit" (recorded by the Ronettes).
Nilsson later worked with Spector when Phil produced "Nilssonny and Cher" singing "A Love Like Yours" in 1974. Spector also produced John Lennon's original Rock and Roll sessions which Harry attended.
Phil was the most important record producer. I really respect him. He always had to be top dog. He was neurotic and eccentric, and I've seen good and bad stories about him, mostly good.
-- Harry Nilsson (1984) 
-  See: One Last Touch of Nilsson
-  Most likely, Spector contributed little or nothing to writing the songs
-  The Age (Melbourne, Australia), Mike Daly (1984-11-08) "Nilsson Sets the Record Straight for Yoko"