Kayla's one best friend, Linz, brunette, slightly lighter than Pia's hair, never says a word. She only talks thru texting on her cellphone. She also never makes any sound of any kind. Do you think she's mute and that's why she uses the phone (just the character not the actress)?
Brother Maynard, bring forth the holy hand grenade!
Mute people use sign language or at least they write something down on a piece of paper. Contrary to what the movie shows, writing is faster than texting. It's also free.
It's just meant to be a joke, because nowadays teen girls text a lot.
Whether writing is faster than texting varies from person to person depending on their skill.
For me texting is way faster AND easier!