I just noticed under Parental Controls, a Smart Limits feature... It was announce Sept 4th and it isn't just for kids. It costs $4.99/month but presumably one could add it on a month-to-month basis, just before an international trip. You use the web to set limits on voice and/or data, so it could be a way around disabling Edge roaming temporarily. You could probably even do it directly from the iPhone...there's a demo but that's in Flash :-(
http://www.wireless.att.com/learn/articles-resources/parental-controls/smart-limits.jsp
Some excerpts:
"Get peace of mind that you can stay in touch with your children, yet wont get hit with unexpected charges on your wireless bill."
"With AT&T Smart Limits for Wireless, you start with an easy online set-up that allows you to determine specifically how and when your child can use the phone. You can set limits on:
Minutes
Text and instant messages
Downloadable purchases (ringtones, games & more)
Times of day or night the phone can be used
Who the phone can call or text (or vice versa)
Internet content access "
http://www.wireless.att.com/learn/articles-resources/parental-controls/smart-limits.jsp
Some excerpts:
"Get peace of mind that you can stay in touch with your children, yet wont get hit with unexpected charges on your wireless bill."
"With AT&T Smart Limits for Wireless, you start with an easy online set-up that allows you to determine specifically how and when your child can use the phone. You can set limits on:
Minutes
Text and instant messages
Downloadable purchases (ringtones, games & more)
Times of day or night the phone can be used
Who the phone can call or text (or vice versa)
Internet content access "