The Global Link has quite a few ways in which you can communicate with other players. In order to keep everything clean, though, sending direct messages through text is not possible. That means even a single message with free-floating words cannot go through, since any message with vulgarities or insults won’t suit the peacefulness and serenity of the Pokemon environment. How you want to communicate depends on who you want to talk to.
In your profile page of the Global Link, there are your Trade Pals next to your Pal Pad friends who have also made a Global Link account. Next to their icon symbolizing their relation to you, there is a button that says, “Send E-Z Mail”. E-Z Mail is a feature where you can pick a prearranged message and insert your own words into it, which are also provided. The selection is kind of limited, which explains why people don’t use it too much, especially between strangers, like Trade Pals.
The other way of indirect communication appears through the Dream World. It is very tough to find your Friends or Trade Pals, since there are about 1 million accounts made in the Global Link. Finding them is slim to none; the odds are even worse than finding a Shiny legendary Pokemon without hacking. But it’s a good thing to make use of what you have; whoever you can find will make a good friend as long as they are active players. By helping them with their world, they can be notified of it and help you with yours, thus making things easier for you and lessening the times you have to go back on. For example, you can help water someone’s Berry garden if it’s becoming dry and earn a few Dream Points on the side, which can help unlock new maps or Pokemon found in there. If there’s a Berry that’s been eluding you, you can check from people anywhere around the world, since in the Dream World Map, there is always a house of one random person with a different Share Shelf each time; they will also be notified if you trade items with them. One more interaction with others is by visiting their house.
You can also see the kinds of Dream World Furniture people place in their houses. In Japan, some items are released early, like the Unova starter Pokedolls, so you can prepare yourself for them. When you enter their house, your Pokemon will leave a mark (if they have a footprint) on the other player’s Footprint Mat. The most recent footprints will show on the Footprint Mat, while all people that have visited can be archived in the “See More” section. If you keep running around, doing favors for everyone, you’re sure to get favors returned, and be sure to add people as your Dream Pals periodically. They can help on a daily basis, and you never know when you will need that help for more Berries or a different item.