The GameBoy Advance Forum is somewhat slow. So people don't usually check it all the time.
Anyways, I can probably answer your question.
The "Game and Watch" was an important piece of Nintendo (and videogames in general) history. Nintendo started off making their "electronic toys" by making arcade games like Donkey Kong, but then they realized that computers were more widespread than people thought. People with digital watches were carrying computers around on their wrists!
So Nintendo made a kind of big digital watch called a "Game and Watch". Instead of displaying a bunch of rectangles that made up passively changing numbers, it displayed interactive stick men and and enemies and obstacles.
They were portable, about the size of a GameBoy Advance, and they needed a controller that was small and cheap and worked well. So Nintendo invented (and perfected at the same time) the digital "crosskey" controller design for them.
They were the grandfather of the GameBoy Advance and GBA SP (I'm pretty sure most, if not all, of the Game and Watch units had a flip-top design, like the GBA SP too). And Nintendo released a whole series of them, with games like Mario and Zelda on them.
I'm not entirely sure about Game and Watch e-cards though. But Nintendo could release the Game and Watch games as e-card programs you could play on your GameBoy Advance. They're certainly small enough. The original Game and Watch units are quite rare, and they've been mentioned lately thanks to things like Smash Bros Melee, so I'm sure a lot of people are curious to see what they're like.
Personally, I think they'll lose a big chunck of their appeal without the antique hardware that came with them (but that doesn't mean I'm not interested in them).