Excel 2007 : Formatting Phone numbers

I need to do an upload and the format of our phone numbers needs to be 999-999-9999

Right now they are all
(999)999-9999

How can I change the phone numbers to look like 999-999-9999
on my spreadsheet I am working on the the phone numbers start on AV595 and go to AV795

Also some of the phone numbers are missing the area code the just look like 999-9999 how can I add in an area code to look like 999-999-9999

this starts on the spreadsheet at AV6 and goes to AV594

Let me know if you need more info.

Thank you!