Formatting question: Importing phone numbers with extnesion

Formatting question: Importing phone numbers with extnesion

Question: When setting up the CSV file to import, I have a list of phone nu,ber both with and without extensions. The DID's are easy as I am using (XXX) XXX-XXXX format to import them. The questio is when importing a number with an extension, what is the best practice for formating this schema to import into AD?
 
Some thought, but I am not sure:
 
(XXX) XXX-XXXX x123
(XXX) XXX-XXXX X123
(XXX) XXX-XXXX x 123
(XXX) XXX-XXXX X 123
 
Which one will work in a dialing schema for mobile device GAB lookup and dial, etc.
 
Any suggestions?

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