As a nice follow-up to my post yesterday about packing for international flights, I came across a good post on T-Mobile global roaming tips over at MobileWhack. The short summary is that you should contact T-Mobile customer service before you leave the country to active global roaming, and know how to put your phone in Manual Network selection mode. For Series 60 phones, the setting is in "Tools > Settings > Network > Operator selection". Keep in mind though, that global roaming rates can be amazingly expensive.
If you like to keep track of multiple time-zones while traveling, you might check out Handy Clock by epocware.
While on the subject of mobile's, k5 has a new post about T-Mobile voice mail security (or the lack thereof) to remind us all that T-Mobile voicemail accounts can be compromised by spoofing caller-id if the account preferences aren't changed to require a PIN code when checking voice-mail.