- How can I check (I need a formula) if a column contains same telephone
number twice or not? It is too slow to check manually (data / sort)

- How could I autoformat telephone numbers, like 040123456 = 040-123
456, so the numbers would be easier to read on screen? I will not copy
phone numbers to any other application, it is sufficient the numbers
will be readable in Excel, so no hard space bars are necessary.