Like written in the title, field formatting using calculation could be very useful.

Eg : Phone number field could be formatted to (406) 987-6543 or 406-987-6543 or 40.69.87.65.43 instead of creating a specific field for just for formatting.

The function could follow the following syntax FormatText (contacts::phone; "(AAA) AAA-AAAA") or something like that.

Such function would be useful. However, there is currently no need to create "a specific field for just for formatting" - you can use an auto-entered calculation replacing existing value.

In somme case it is not possible to use such calculation. Eg : If I want to save only the digits of the phone number, but display them in different format depending on the output (Paper, screen, FMGo, ...)