Secret Friends were the precursor to True Friends and SpeedChat Plus. Toons became Secret Friends by exchanging a code (called a "secret"). Once they were Secret Friends, toons could chat with each other by typing instead of using the SpeedChat. Toons who were not secret friends would only see animal noises (like "meow mew mew meow" for cats) when non-Secret Friends were using chat. There was no open chat until SpeedChat Plus was introduced.
Like True Friends, a toon could generate Secret Friend codes by clicking on the blue circle in the upper right corner of the Friend list. If another toon typed in the code within 48 hours, the two would become Secret Friends. Secret Friends' names showed up in blue on a player's Friend List and on their Secret Friends' nametags.
The Secret Friend system was designed for people to exchange codes in real life. However, many players found ways to exchange codes with people they did not know.
Some fan sites had forums where posters could exchange Secret Friend codes.
To communicate to non-Secret Friends that they wanted to become Secret Friends, players would use the SpeedChat phrase "Please be my friend!" and then type into the chat, which would show up as animal noises to the non-Secret Friend. If the other player understood that the animal noises represented chatting, he or she would say, "OK." As of 2007, it was against the Toontown Online rules to exchange codes in-game.
There were two methods of telling other toons codes in the game: SpeedChat and Estate.
To communicate a code using SpeedChat, toons would say SpeedChat phrases that began with the same letter as the letters in the code. They would communicate numbers by jumping a certain number of times. For example:
"You are awesome!" [Y]
Jump twice 
Jump seven times 
Jump five times 
The other toon would then understand the code was yr2 g75, input the code, and both toons would become Secret Friends with one another.