MsgBox FormatNumber$(&H7FFFFFFF, , , , vbTrue)

Note that results depend on locale settings: most VB functions are locale aware, thus you get results according to which country the computer is located at.


If you wish to force to have commas every X character, you have to do it by yourself.

Code:
Public Function Comma(ByVal Expression As String, Optional ByVal Spacing As Byte = 3) As String
    Dim lngA As Long, lngLen As Long
    If (Len(Expression) > Spacing) And (Spacing > 0) Then
        lngLen = (Len(Expression) \ Spacing) + Len(Expression) + ((Len(Expression) Mod Spacing) = 0)
        Comma = String$(lngLen, ",")
        lngLen = lngLen - Spacing + 1
        For lngA = 1 To Len(Expression) \ Spacing
            Mid$(Comma, lngLen, Spacing) = Mid$(Expression, Len(Expression) - (lngA * Spacing) + 1, Spacing)
            lngLen = lngLen - Spacing - 1
        Next lngA
        lngLen = lngLen + Spacing - 1
        If lngLen > 0 Then
            Mid$(Comma, 1, lngLen) = Left$(Expression, lngLen)
        End If
    Else
        Comma = Expression
    End If
End Function
MsgBox Comma(&H7FFFFFFF)