Actor Allusion: In Scream 4, Gale and Rebecca's conversation has Rebecca bring up how surprised she is that Gale and Dewey's marriage worked as well in real life as it did in the Stab movies. The actors who play Gale and Dewey, Courteney Cox and David Arquette, are married. Also becomes Harsher in Hindsight when one remembers that the two of them separated not long after filming on Scream 4 was wrapped — and that the main thrust of Dewey and Gale's story is that their marriage is falling apart.
The Danza: Emma Roberts' character is named Jill Roberts.
Dawson Casting: All of the teen characters in the original are played by actors who were old enough to drink at the time.
Enforced Method Acting: Craven made sure that none of the actors had met Roger L. Jackson prior to filming and the telephone scenes were filmed with him actually on the phone.
The first film was originally called Scary Movie (no relation) and remained so throughout most of its production, but Harvey Weinstein changed the title at the last minute. Wes Craven was miffed at first, but after a while he grew to love the new name.
Scream 4 apparently underwent a lot of this from the Weinsteins before its release, including most of the script changes. The DVD Commentary alludes to this on several occasions, particularly on noting that the movie was originally due to end with a "We got a heartbeat!" scene involving Kirby.
It isn't much of a stretch to imagine how NancyDrew could hatch a murder scheme, given that she's solved several over the course of her career. But who ever imagined that the kid from Signs would be the accomplice?
Also, in Jay and Silent Bob Strike Back, the duo stumbles upon the the filming of a Scream movie. The first movie in the series had a poster for Clerks, a movie in the same continuity as Jay and Silent Bob. Though it's not explicitly stated to be a Scream film, it could have been a Stab movie, as some fans think. Jay and Silent Bob themselves show up in a blink-and-you-miss it scene in Scream 3.
No Export for You: Scream 4: You want to hear more of Wes Craven, Hayden Panettiere and/or Emma Roberts? Luckily they're on the DVD Commentary track (as is Neve Campbell, who literally phones in her contribution)... what's that? You live in the UK? And it's not included on the Region 2 release there, either on the DVD or blu-ray? Well, if you don't have a multiregion player... or if you can't be bothered to import the French R2 release (which does have the commentary - and an English language track)...
The Red Stapler: Caller ID systems became so ubiquitous after this film came out (any guesses as to why?) that it was even lampshaded in the sequel, where Sidney has one and uses it to catch a Ghostface-imitating prankster.
Neve Campbell and Matthew Lillard, though only for 2 years.
Sequel Gap: Scream 4 came 11 years after its predecessor (which incidentally is longer than the time it took to make and release all three previous films) and thus takes shots at basically everything that happened to horror films in-between.
At the end of the first movie, Billy hitting Stu with the phone in anger was unintentional, as the phone accidentally slipped out of Skeet Ulrich's hands due to the fake blood. Stu screaming "You hit me with the phone, dick!" was actually Matthew Lillard's reaction.
In the scene where Sidney attacks Billy with an umbrella, Billy's actor, Skeet Ulrich, got legitimately injured. When he was hit by the umbrella, the stuntwoman playing Sidney couldn't see where she was aiming and wound up hitting a wire in his chest he had gotten during surgery at a young age. Touching it ends up causing him some pain.
In Scream 3, when Sidney jumped over the bar and stabbed the killer in the back with an icepick, Neve Campbell missed the pad that she was supposed to plunge the pick into and actually hit flesh. Scott Foley's scream is genuine.
Technology Marches On: Or more specifically, access to technology marches on. When Billy drops his cell phone while comforting Sidney after her first attack by the killer, he becomes an immediate suspect because the killer was using one. Back in 1996, cell phones were still rare enough that this would look suspicious. Today, not so much.