SOLVED. YA Early 2000s Friends writing notes

[Laura]

I think 3 or 4 friends in high school who write notes to one another for am entire year, because one of the friends has taken a vow not to speak. The book is written as their notes to one another.

[Laura]

Ok literally I remembered it 5 minutes after I posted this:

The Year of Secret Assignments, by Jaclyn Moriarty

[Rainbowheart]

Glad you found it!

The Year of Secret Assignments for the link.