For music, I'm thinking one of two things: Either a music box (possibly containing a miniature instrument orchestra like Sauce Bauss suggested) or a tiny portrait in a case (think those old-school cigarette cases) depicting a band.

For advertising, I'm imagining a portrait that runs into other portraits, like Sir Cadogan. They somehow keep finding their way into other portraits, shouting out advertisements at passersby. They keep getting into fights with other members of the portraits and sometimes other advertisers. For some reason I'm imagining the advertisers are usually goblins (or made by goblins).

Alternatively, the portraits are being paid to randomly advertise products. A lot of times, they'll be doing so with a very strained smile. It can feel unnatural, like the advertisements the wife does in the Truman Show.

I particularly like the idea of the internet being made by spiders. IIRC, Steelbadger's HP/ASoIaF crossover had the reincarnated!Harry misunderstand the internet as a giant web ("www." = "world-wide web") so having a library completely covered in spider webs in Hogwarts and the Ministry of Magic seems like it can be one of those puns Rowling likes to do (Spellotape/Sellotape (British Scotch Tape, for Americans)).

If you wanted to make fun of Twitter, you could have a variation of the Avis spell that summons birds, where small blue birds will fly out to those who have "followed" you to relay a message. I figure that who follows a person is determined by who casts the spell, so there are "spam blocker" charms that swat them away, like around Hogwarts.

 

Hogwarts has enchantments which protect it from Twitter? Truly it is the most magical place.

 

What?! Steelbadger’s asoiaf xover? Sauce!

 

Sorry, I was thinking of Cxjenious's The Prince Who Was Promised.

 

And has inexplicably massive cans proportional to her size.

 

I haven’t been this blueballed since i was 18, dammit.