Taken from JeffH's Crackberry.com post.
"Why doesn't my Blackberry update the time correctly when I travel across time zones?"
This question comes up once or twice a month, generally from a new user who is dumbfounded their expensive new smartphone can't do something their last three dumb phones did automatically. I'm offering this post to elaborate on the Blackberry FAQ, cited below, and to offer a real life example of how the Rim technique works. I hope it will clear up some of the confusion around this topic, and help new users get the most from their phone. Your comments are welcome. I'll be happy to correct any mistakes you find.
An ordinary cell phone without an integrated calendar doesn't have to care about appointments and so can automatically switch time zones, by simply displaying the network time. That's what new users are accustomed to. Why doesn't the Blackberry behave the same way? Because Blackberry's have integrated calendars. The calendar and the clock use the same time reference. If you change the clock, you change the time reference for appointments. Thus, Blackberry's don't change time zones automatically because that would cause appointments to be shown incorrectly, if the appointments were entered in the wrong time zone. Why would anybody enter an appointment in the wrong time zone? Because Outlook doesn't let you have more than two time zones available at any time, so people who put in appointments using Outlook and do business in more than two time zones are going to have a problem, or else have to do the time zone math when they enter appointments. And, there's the natural but incorrect tendency to think of 2:00pm as 2:00pm, wherever you are. If you input your appointments using the Blackberry calendar input screen, all the time zones are available to you. It's just Outlook that makes it difficult. A few typical questions and an example will illustrate the problem and the solution.
"I had a 2:00 pm appointment in LA. I put the appointment on my calendar in Atlanta for 2:00 pm and when I got to LA and manually changed my time zone, it changed the time of my meeting by three hours! Why doesn't RIM fix such a horrible glitch?"
Because it's not a glitch. The problem is you put the appointment on your calendar in the wrong time zone. If you're on the east coast, don't put an appointment on the calendar for 2:00 pm eastern and expect it to read 2:00 pm pacific. It'll be off by three hours. Put it in as 2:00 pm pacific. When you're in ET, it'll show up as 11:00 am. When you arrive in LA and change to PT, your 2:00 pm PT appointment is correct. It's designed to be right when you cross time zones.
"I didn't put it in as 2:00 pm Eastern. I put the appointment in Outlook in local time."
Even though Outlook 2003 doesn't explicitly associate a time zone with an appointment when you enter the appointment, it's still made with the time zone setting from your computer. Eastern, in this case.
"But can't you go to options/date/time and set the time source to network? Wouldn't this cause the Blackberry to update to the new time zone?"
No. With Date/Time source set to Network, the Blackberry pulls the time from the network, but still applies the GMT offset for the time zone you selected. It will update your minutes, not your hours. You still have to change the time zone manually.
Here's a worked out example:
Time Zone: ET
Date/Time Source: Network
Sitting at my desk in the Eastern time zone with the Blackberry options as shown, I enter an appointment on my Blackberry calendar for 1:00 pm Central, using the time zone dropdown in the Blackberry Calendar entry screen. When I save the appointment, it shows up on my Blackberry Calendar (and Outlook) as 2:00 pm, correct for Eastern time. I ride to the airport, get on the plane, and turn off my phone, which is still set to Eastern time and Network. I fly to Alabama, which is in the Central time zone.
We land in Huntsville, and the Flight Attendant announces the Local Time is 10:16 am. I turn on the phone. The phone displays 11:16 am on the Home Screen. I look in Date/Time Options. Time Zone: ET. Time: 11:16 am. Network Time: 10:16 am. I change the time zone to CT. Now Time reads 10:16 am. The phone shows 10:16 am on the Home Screen. And the calendar correctly shows I have an appointment at 1:00 pm Central time.
I agree, it would be better if the phone "knew" I changed time zones. But it doesn't. All it knows is that there is a 1-hr discrepancy between "time" and "network time." It could prompt you with something like "The local time is different from your Blackberry time by 1 hr. Would you like to change your time zone to CT?" Now that would be smart! And better than having to change it manually. Another solution would be to decouple the calendar from the clock. Again, phones without calendars can just display network time and not have to worry about time zones. That's why older phones can do this, and naturally, users expect a newer, smarter phone to do it, too. But Rim's implementation works, as long as you enter appointments in the correct time zone.
"O.k., I got all that. But my Blackberry does automatically change time zones. It just doesn't change to the correct one! It keeps changing back to my home time zone when I'm traveling. Why is that?"
In Desktop Manager/Synchronize, you have the option to "Update Device's Date and Time" when you sync. If this box is checked, every time you connect to Desktop Manager, either to sync your Blackberry or to back-up, Desktop Manager will set your Blackberry to your computer time. If you left your laptop set to your home time zone, then synching will cause your Blackberry to change back to your home time zone. If you select "Network Time" as your Blackberry time source, you don't need this setting. Unchecking it will keep Desktop Manager from changing your Blackberry time.