Connect select boxes using javascript

We have one select box containing countries. The form also has a select box containing phone country codes 1. Populate the phone country code based on the countries of the first list 2. Using jquery connect the select fields so that when a country is chosen in the first select box, utomatically select the correct country code in the second select box PS if the user changes the country code in the second box, no change should occure in the first box (ie. only one way connection)