The most common and most likely answer to this crossword clue is the 4 plus 2 plus 5 letter word CALL TO ORDER
I've seen this crossword clue in The Daily Telegraph
C
A
L
L
T
O
O
R
D
E
R
Buddy explains!
The straight part
We know that "it’s open for business" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s open for business = call to order.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.