First of all, I assume you want to be at least able to get your email while roaming.

Now, one way would be to keep the device unconnected, and connect only when needed. Thing is granularity for billing a data connection is about 10kB, and if you aren't connected permanently, for each connection using less than 10kB you are actually billed as if you used 10kB. So it makes more sense to keep the device permanently connected just so it doesn't waste unused traffic.

HOWEVER, there are a few things to watch out for:

Best surprise ever was when getting off the plane at 8 o'clock in the morning and suddenly getting 5.5MB of data traffic out of the blue. 33EUR, gone in an instant. I don't mind some traffic (checking email periodically, I need it even when roaming), but 5.5MB just like that? That got me scratching my head (and swearing). Realized afterwards that it's the update feature kicking in (all repos enabled). So headed off to App Manager and disabled all repositories (just so I don't get additional surprises the next morning).

Some other things to watch out for are RSS feed readers, weather and email apps, and all other apps that update automatically.

Second surprise was using OVI Maps and having the application start downloading updates to the maps I already had installed prior to traveling. Great. With no access to wifi, I had to close it down. Big minus to Nokia for not implementing an offline setting for Maps. Best thing before traveling would be to do a sweep of your destination in OVI Maps so it downloads any updates when you're connected to your home connection. Just zoom in at city level and pan around.

Personal Dataplan Monitor (the widget) is your friend when roaming with a data connection. It allows you to keep an eye on things. Install it from extras (or extras-testing or dev, not sure) and put it up on your desktop. One glance and you'll know if you're staying within limits. Before boarding your plane it's a good idea to reset the traffic counter in Settings > Phone, so that you can monitor your traffic at a glance.

If you have any additional tips please post them here.

could you please write this in a bit another form to maemo wiki?

http://wiki.maemo.org/

for example something like

http://wiki.maemo.org/Roaming_tips_and_tricks

or similar. If you do that, link the page here and I can tag it to correct category etc...

e: and forgot to mention but you have very good briefing there how to minimize roaming data transfers.

Hi ossipena. I'll do it later on today after work That's a good idea. I'll post back here afterwards.

Article is available here:
http://wiki.maemo.org/Roaming_tips_and_tricks