Location: Goldenrod City

Method:
The Pokémon Communication Centre starts off as seeming like an ordinary Pokémon Centre, but as you activate the Mobile Adapter, the centre opens up. In it, you will find a special Trade Corner, which allows you to trade with various people wirelessly across Japan. This acted in a similar way to the Global Trade Station allowing you to put Pokémon you want up and Pokémon you have up for trade. This cost 10¥ per trade

It also included the Pokémon News Network, which gave various updates about the game, progress in your local areas, as well as details on special downloads. This required a service charge of 100 Yen a month

You can also trade and battle with your friends upstairs online in the Pokémon Communication Center

In the main menu, the precursor to the Pokémon Global Trade Station was available. This feature allowed for you to put up Pokémon you had for Pokémon you desired for people to trade with you across Japan or to search for a Pokémon you need.

This cost 10¥ per each trade.

Location: Route 42

Method:
Located above Route 42 is the first iteraton of the Battle Tower. In the Japanese version, this unlocked with the use of the mobile Adapter and allowed for battle with people across Japan. It also tracked various people, the amount you battled and other such statistics

Restrictions
10 floors: Level 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
Pokémon: Cannot use Mewtwo, Mew, Lugia, Ho-Oh, Celebi
Cannot use two of the same Pokémon or hold item.

Within the English release, this kept the restrictions and levels, but included more AI trainers having you face up against 7 per floor. These trainers used Pokémon from a random selection and you were given Protein, Calcium, Carbos, Iron and Zinc whenever you defeated all seven trainers on the floor.

This service cost 10¥ per round

Mobile Stadium was a feature that connected to Pokémon Stadium 2. Each day in half hour increments there were distributions of Tournament data; battles that were held in the official tournaments across Japan. With this, you would then be able to watch the tournaments in Pokémon Stadium 2. Almost a predecessor to the VS Recorder of later games, you also have the ability to battle against the teams in this battle

This service cost 20¥ for each use

Duration: March 29th 2001 - May 29th 2001 & August 1st 2001 - August 28th 2001

Method:
To acquire a GS Ball you have to connect the game to the mobile phone with the Pokemon Mobile Phone System GB. This cannot be done in the US. You must have all 16 badges, beat a minigame, and complete a quiz to have the attendent at the Pokemon Communication Center in Goldenrod City give you a GS Ball. Once you have it, take it to Kurt to have him inspect it. After 24 hours he'll tell you about a strange presence in the ball before dashing outside. Follow him and he'll say Ilex Forest is uneasy and that you should check it out with the GS Ball.
The trees will be rustling in the forest. Take the GS Ball to the shrine. When asked if you want to put the GS Ball in the shrine, say yes and Celebi will arrive to challenge you. Celebi holds no special items. Grass/Psychic is weak to Fire-, Flying-, Ghost-, Dark-, Ice-, and Poison-types and has a double weakness to Bug-types but offers good STAB and learns powerful moves like Giga Drain, Psychic, and Solarbeam. Because you need all 16 badges to fight it but is faced at a low level of 30, it would be wise to bring something that can inflict status before it uses Safeguard but not OHKO it. Be prepared for a long fight as it can heal with Recover.

Celebi Level 30

OT: Yours ID: Yours Hold Item: None

Heal Bell Safeguard Ancientpower Future Sight

Duration: January 27th 2001 - December 14th 2002

Method:
In addition to the Togepi egg from Gold and Silver, players can obtain a second egg in the Crystal version. This egg can hatch into any of the baby Pokemon, allowing players to potentially receive their favourite Pokemon far earlier in the game than normal, with the special move Dizzy Punch as an added bonus. This page details how to get it in both the Japanese and International versions.

Japanese Version
In the Japanese version, players get an Egg Ticket from the Day Care Man which must be redeemed at the Pokemon Communication Center in Goldenrod City. Any of the baby Pokemon have a 50% rate of being shiny.

Pichu Level 5

OT: Yours ID: Yours Hold Item: None

Thundershock Charm Dizzy Punch

Cleffa Level 5

OT: Yours ID: Yours Hold Item: None

Pound Charm Encore Dizzy Punch

Igglybuff Level 5

OT: Yours ID: Yours Hold Item: None

Sing Charm Defense Curl Dizzy Punch

Tyrogue Level 5

OT: Yours ID: Yours Hold Item: None

Tackle Dizzy Punch

Smoochum Level 5

OT: Yours ID: Yours Hold Item: None

Pound Lick Dizzy Punch

Elekid Level 5

OT: Yours ID: Yours Hold Item: None

Quick Attack Leer Dizzy Punch

Magby Level 5

OT: Yours ID: Yours Hold Item: None

Ember Dizzy Punch

Duration: 2001

Method:
This distribution ran for a time in 2001 and allowed for you to receive the special Mirage Mail, which is unavailable in the games otherwise