Custom Validation rules

Hi all,

I have a book with multiple sheets, each holding entries based on customer telephone number. I would like to restrict the values that a user is allowed to enter into the ID field (column A). The values i want to allow are:

- number strings 8 number long, but MUST start as 200, i.e. 20012345,
20054321, 20029292, etc.
- the following text strings: 'free' & 'faulty'

I've been reading up on validation rules on Excel, but cannot see examples that allow something on the lines of what i need, which is a mixture of text and numbers, but the numbers will vary so i cannot specify these before hand.

Hope some1 can help.

Thanks