Maybe you can use BitPIM, or SyncMate, MissingSync, possibly QPST or QXDM etc... to sync the contacts to your computer...(a good idea is to create a new user profile, so it won't mess up YOUR contacts)...
Once you sync the contacts, view your address book, and look for MOM, then call that number from your phone and let them know that you found the phone. (if there is no MOM look for HOME, DAD, or something similar.
You can also call the market where your mom found the phone to see if the owner went there looking for it.
I am sure that there is a way to pull the phone book out with ADB as well...
...
Another more dramatic option would be to run an RUU, after update, type ##786#, and check the MSID #...This person may have already attached an old or new device to their line because they don't have the EVO...
You can then call them, and tell them you found the phone. Make sure to apologize for erasing their phone, but explain why you did it.