Prefix matching while importing large CSV file
DRY -- a database principle -- "Don't Repeat Yourself".

Instead of copy the data over as you load it, look it up when you need it.

SELECT c.contact, tz.state, tz.timezone
    FROM contacts AS c
    JOIN timezones AS tz  ON tx.prefix = LEFT(c.contact, 3)


Caveat:  This assumes that you won't modify the timezone after assigning it to a contact.

What is the application?  Perhaps some form of call center?