How to modify AD attribute in variable assign expression?

Is it possible to modify an AD attribute (phone number) to a different format in an variable assign or does this require an iRule.

 

For example in AD the attribute "telephoneNumber" is set as "+12 34567890"

 

96171b94.session.ad.last.attr.telephoneNumber 13 +12 34567890

 

I want to remove the + and have the number in standard format, "001234567890" at the moment we can assume that all numbers will start with +12 and move on from there.

 

Does anyone know how to achieve this?

 

Cheers, AM