I lost my phone..

As temporary or permament replacement, I found my dad's old Sony Ericsson T68i in the closet. A couple years ago when I was curious and put a Cingular sim card in, it wouldn't work because it was an 'AT&T' locked phone from back in the day. Now that we've come full circle with company branding, will the phone accept a current replacement sim card? If not, will ATT unlock the phone for me?

The phone is small, don't have to flip or slide it and has bluetooth, so it fullfills the requirements.