Can you give me examples (backed with citable sources) of instances when one GM made a call to another GM for the sole purpose of getting a "free opinion"?
Sure, I'll give you two (you probably don't know one of these stories):
These have to do with the 1988 NBA draft, at a time where Coaches served as quasi-Gm's themselves
During the early summer, the 76ers let it be known that had about had it with Charles Barkley and would be willing to trade him.
The Clippers had the first pick AND the sixth pick of that draft (The 76ers had pick #3) and they had already agreed to terms with Danny Manning. (to be the #1)
But they contacted Philly, thinking maybe they could work something out.
Philly wanted two lottery picks for Barkley and the Clips had them.
But they were only willing to part with the #6 pick in 1988 (and one in another year) - they really wanted Manning,
They danced around but neither moved, so, the trade did not get done.
But, because they were talking and learned what each party needed, on draft day, the Clips called Philly as the third pick approached and worked out a deal where the Clips gave Philly a future first in order to move from #6 to #3. So, the Clips wound up drafting Hersey Hawkins and sending him to Philly for Charles Smith (who they selected third).
It wasn't what they started out to do, but because they had numerous conversations, they were able to agree on a different deal - because it never hurts to keep everyone informed.
The second example (from the 1988 draft) involves "communicating for nefarious reasons"
Background:
Back in the 80's, there was a predraft "tournament" for seniors entering the draft.
Each year, two NBA coaches were selected to coach the two teams of seniors.
In the early summer of 1988, those two coaches were Don Nelson and Cotton Fitzsimmons (who knew each other quite well - Nelson actually WAS the GM and Cotton might as well have been and held that position in the 90's - it was HE who arranged the eventual Barkley trade not to the Clippers, but to the Suns ).
They had a "bird's eye view" of these seniors and both were impressed with a guy who was not so highly regarded: Mitch Richmond
So, the draft went Manning, Rick Smits, Charles Smith and then came New Jersey, the Warriors, LAC (who would be drafting Hersey Hawkins for Philly) and then Phoenix (where Cotton was coaching).
Nelson knew he wanted Mitch, so, first he called New Jersey on some pretext and found out that they were going to draft Chris Morris. but not with great enthusiasm. From the discussion, Nelson deduced that if Fitzsimmons called seeking to move up to #4, the Nets would listen.
So, then he calls Cotton to tell him ostensibly that Barkley is on the block. During the conversation, he let's "slip" that he had spoken to the Nets and that New Jersey is super high to take Morris and "fibs" that he is looking seriously at Rony Seikaly at #5.
So Cotton does not call New Jersey to try to trade up and get above Nelson, because Nelson has made him believe that he will be able to get Richmond at #7.
Then, when Nelson takes him, he tells Fitzsimmons that at the last minute, he soured on Seikaly.
Fitzsimmons winds up with Majerle at #7, but without making those calls, Phoenix likely moves up, drafts Mitch and he never becomes a King.
to help us out for it. He has an exit if he doesn't want to be here. Take it. Please. We beg you. Go away. 
