I have seen this sequence so many times, and one thing it does it captivates you since the beginning till Drew Barrymore dies. This opening sequence is like a shot movie in itself. It has a beginning, middle and end (mind you not a pleasing end).

I like how it starts innocently enough. We're like Drew's character in that we don't know who's calling, don't know what their motive is, etc. She's going to watch a "scary movie", so that puts the scene into context. The chit chatter takes a flirtatious tone until we're hit with the menacing thought of being stalked ourselves. All the previous dialogue in the scene then takes on a new context; it's no longer innocent and appears to have intent. Asking what her favorite scary movie was, does she have a boyfriend, etc., all comes back to haunt her as the killer demonstrates total control and manipulates her. Other things that are going on that help contribute: the popcorn adds a bit of a literal pressure cooker. The parents coming home add suspense - will she or won't she make it out alive? The phone itself, a vessel of terror for her character, does double duty as her parents go to make a phone call, hearing her gasping voice on the other end, unaware of what's happened. As Mragendra pointed out, it really does have a beginning, middle and end, the turning/mid point being the killer's revelation that they may be watching, to which the dramatic question "will she live?" is emphatically answered by its end. The fact that Drew Barrymore received a top billing for the movie really added to the shock value. I remember seeing this before I moved to Las Vegas, telling my friend about it upon arriving, then watching it with him. His first words afterwards regarding the opening: "I wasn't expecting that."