The phrase "separate call" is correct and usable in written English.
You can use it when you are talking about different phone calls (especially ones that have different topics). For example: I made a separate call to my friend to tell her the news.
A separate call has gone out to hold a mass party and protest in Trafalgar Square this Saturday at 6pm.
Mrs. Merkel has rejected a separate call from Luxembourg and Italy to create a common euro zone bond.
He would also place a separate call each day to his father, just so dad would not feel left out.
"We need to have a pristine reputation," Hamilton E. James Jr., the president of Blackstone, said on a separate call on Thursday, while discussing regulation.
The S.E.C. had a separate call with Knight and the New York Stock Exchange, according to people briefed on the call.
Amnesty International USA's executive director, Steven Hawkins, called for "a prompt, thorough, independent and impartial investigation" in the letter, which he noted was a follow-up after receiving no response to a separate call on Emanuel in February.
By moving a right-handed reliever like Wendell or White, the Mets would open a spot for Jerrod Riggan, a rookie right-hander who has been impressive in five separate call-ups this season.
"I made two separate calls to see what would happen".
She'd fielded three separate calls that day from Cecil Harkness.
There were three separate calls between Clegg and Miliband prior to the reconvening of the talks.
In separate calls, the senators urged Mr. Christie to help persuade Senator Jeffrey S. Chiesa, Republican of New Jersey — newly appointed by Mr. Christie — to vote for the bill.
