I have a corporate Blackberry on ATT/Cingular service in the US, and I have to turn it off, take out the battery, lift the SIM card off the contact pad, then replace it all and turn it back on upon return to the states from any extended overseas trip, as do most of my staff.

At least this gives me something to do while I wait in the line for immigration.

So the Treo is not alone in this undocumented feature.