FreeFile Function

Syntax:
FreeFile[( )]
Group: File
Description:
Return the next unused shared stream number (greater than or equal to 256). Streams 1 through 255 are private to each macro. Streams 256 through 511 are shared by all macros.
Example:

Sub Main
Debug.Print FreeFile ' 256
FN = FreeFile
Open "XXX" For Output As #FN
Debug.Print FreeFile ' 257
Close #FN
Debug.Print FreeFile ' 256
End Sub