One way is to make a calculated field, = Case (Available, Phone Number). Then, make the value list based on that calculated field.
I'll give it a try and let you know. Thanks.
I'm not having much luck here. When I try to use the =Case it doesn't seem to find anything. When I"m in the Layout I get a "no values defined" message.
It should be a simple if, then function. If Available = Yes, then show Phone Numbers, but that's not doing anything either. It tried swapping "Yes" for "1" or "0", but that isn't it either.
I have calculation results set to text.
I should have been much clearer. You need to define a new field in your table, a calculation field, with the formula similar to this:
Case ( Available = "Yes", phone_number )
Your value list will be based on this field. The real question is how to automatically marked the used phone numbers as 'Not Available'. This could also be a calculation, depending on the structure of your database.