My voicemail is full, got bitches screamin' inside of envelopes
And they tryna mail ‘em to me

from Royce Da 5'9" (Ft. Eminem) – Writer's Block Lyrics on Rap Genius

Meaning

Because she cannot leave a message via voicemail (due to the fact that she has already left an infinite amount) the only other alternative to contact him is the classic way: writing a letter.

PROBABLY A LOT OF CAPS LOCK LETTERS, EXCLAMATION MARKS, AND FUCKING DERAGATORY STATEMENTS IN THERE!!!!

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