Wireless Battling & Trading
The most notable difference between the original Pokemon Yellow to the Digital Version on the 3DS is the additional inclusion of the Wireless Battling and Trading Features.
Back when the game was originally on the Nintendo Gameboy, you actually had to buy cables that you would hook up to your Gameboy and a friend's Gameboy just to be able to Trade or battle with that person. It was hassle that many older Pokemon Fans will never forget, but now, on the Digital Copy of Yellow, all of that has changed.
All you have to do now is go to the Cable Club in each Pokemon Center as you would with the cables inserted in the original copy of the game, and the game will activate a prompt (shown above) asking if you would like to invite a friend or join a friend. Once you decide and connect, the General Cable Club features, including Battling and Trading wirelessly, will continue. (If the connection is broken, the features will end.)
This was feature that wasn't available when the first copies of Pokemon Yellow were released, but now, twenty years later, technology has advanced to where Pokemon Trainers won't struggle when wanting to battle or Trade with their friends.