Formula checkbox for certain entries over a character limit

Hello,

I have an application tracking quality defects, one of the fields for capturing information is the catalog unit. that catalog unit is typically 7 digits, for special units where we specialize a standard catalog unit for customer speicifications we typically add 5 digits on the end. I was able to make a formula for seeing if something was special by having 

[Catalog Number]>999999999

unfortunately, they are starting to use alpha characters on these unit numbers now. is there a formula that can do what I have done prior but also allows for characters to be entered?

thanks,