The day after the state dinner with the president of France, the president is in the Oval Office and is trying to call a florist. He picks up the phone and asks "How do I get an outside line?" However, several days before that, he made a call from the residence (and I'm pretty sure his assistant wasn't there to make the call for him) to Sydney at her sister's apartment. Therefore, he had to know how to get an outside line since he had just done it a few days previously.