It is an automated survey from Sprint usually regarding recent customer service issues you had.

I've been getting calls from this Los Angeles based number as well. No message left. When I called back (after hours) it rang 4 or 5 times and than an announcement ..."This number not currently in service."

I received a call from this number today, no message was left either...

Received 3 calls from this number today, approximately 4 hours between each.  No message left for me.  When I called back (after hours) it rang 4 or 5 times and than an announcement ..."This number not currently in service."