I am well aware of the excellent Custom Number Formula:
[<999950]0.0,"K";[<999950000]0.0,,"M";0.0,,,"B"
Which abbreviates #,000 numbers to #K, #,000,000 to #M etc...
However, I am looking for a formula that will leave numbers below 1000 unchanged.
For example, the number 999 will remain 999 but the number 1,001 will abbreviate to 1K.