Instructions
Start "Pokemon SoulSilver." Press the "Start" button and view your character's Trainer Card. Your unique trainer ID is the five-digit number shown at the top left of the screen. It is the key to unlocking the phrases.
Write down the five digits, then travel to Violet City and enter the Pokecenter. Speak to Primo, the man standing next to the stairs on the right of the center. He will ask you to enter a phrase.
Open the web browser on your PC and navigate to the Pokémon Secret Phrase Generator website. Enter the five-digit code under "Trainer ID" and click on the radio button next to "HeartGold or SoulSilver."
Click the radio button next to "English Version." Click "Send." All phrases for the wallpapers and eggs will be displayed.
Enter phrase that corresponds with the item you want to unlock. These phrases are unique to your Trainer ID, so using a list of phrases others post on the Internet won't work. Once you have entered the phrases, Primo will reward you with the items. You can repeat until you have unlocked all the wallpapers and eggs.