>My father just bought a Sony Vaio VGN-UX380N which has a built in
>Cingular SIM, and supports WWAN access.
That's built-in Cingular wireless. The SIM is removable.
>He wants to use this overseas
>for wireless data access. Is there any information about where this
>will and won't work? What about roaming on other systems?
Cingular has information on international roaming.
Data roaming is very expensive.
Coverage maps at GSM World
<http://www.gsmworld.com/roaming/gsminfo/index.shtml>
His best bet is to get his Cingular wireless unlocked by Cingular, and
buy local SIMs for data (and voice) when overseas.
See the Cingular FAQ below for more information.

Signature
Best regards, FAQ FOR CINGULAR WIRELESS:
John Navas <http://en.wikibooks.org/wiki/Cingular_Wireless_FAQ>