I'm a former employee of Sprint and I used to have to deal with the fraud guys a lot. Important tip: do not wait for these guys to get back to you. Keep on top of them if you want anything done.
It's sad but true: at Sprint only the squeaky wheel gets the grease.
EDIT: As a side note, I'm surprised this chick needed your SSN at all. I would pull up accounts for people who were obviously illegal immigrants all the time and they always had 9999 as the last four of their SSN. It's not company policy by any means, but it's common practice.
Thanks for the heads-up. Monday will be the one-week mark from when I originally called them, so I'll definitely hit them up to make sure they've been checking into this. They said I would receive a letter but I really don't want to wit for snail mail, unless they factored that into the 7-day estimate.
File charges for identity theft and fraud. Prosecute and then sue for civil damages. Given the name, proximity to the border, and the use of another's SSN, this looks like it could be an illegal alien who may have randomly picked your SSN out of the air when she was asked for it. So call the INS too and tell them what has happened and give them her address.
I've contacted my local PD and was basically told that I need all of Sprint's info until they can begin an investigation. I do have an officer to contact when I do have that info, so that's at least a step in the right direction. Basically I'm just waiting for Sprint.