I just setup my Nexus 4 on CC. I called to setup access and the told me I'd get a callback the next day. I got that call and these are the settings they gave me:
Name: cci
APN: att.mvno
Proxy: 66.209.11.32
Port: 80
username/password/server: not set
mmsc: http://mmsc.cingular.com
MMS proxy...