call from a known "unkonwn" number

The school year ended in a slow, not-so-lesson-filled wind-down and pack-up. On the final day, one of my students - who had been a challenge for herself, her family, and me, all year - wasn't present. Later that evening, I got a voicemail from her:

Hi Ms. H,
I missed being in school. Call you later, bye.
And you are a special person to me.
You're the only friend I got.
Bye.

And later she called back and left another message...

Hi Ms. H, Um, sorry to call you, but please don't tell my mom.
I didn't have a chance to say goodbye Friday. Please send me your address so I can send you a postcard.

Then she started singing:

Trying to say goodbye
Ms. H I'm sorry I caused you all these problems
You feel like a mother to me
I feel like a daughter to you
It feels like I didn't when I was growing up
But Ms. H, I'm sor-rr-rry
I'm going to send you a letter
When you send me your address
Ms. H I love you with all my heart
But I'm gonna pray to God that God lets me stay at your school.
Bye Ms. H Sorry I didn't get to say goodbye.
Don't tell my mom, Ms. H.
That song's for you, just for you.
Love you, Ms. H. Bye.