Syncing your calendar on your iPhone and your laptop can be accomplished in seconds thanks to the MobileMe service from Apple. The online service uses the "cloud" effect, which is a server that sends your updated and new information to all devices that are set up for the synchronization. MobileMe not only syncs your calendar; it syncs your address book and email.
Sync using MobileMe
Press the "Home" button on your iPhone. Slide your finger across the screen to unlock the phone, then tap the "Settings" button on your screen. Tap your email address tab under the "Accounts" section, then tap the "Account Info" tab.
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Type in your name, password and a description of your MobileMe account. When finished, tap the button in the upper-left corner to return to the previous screen.
Slide your finger across each tab. Make sure each tab ("Mail," "Contacts," "Calendars," "Bookmarks") is set to "ON." Tap the button in the upper-left corner of the screen to return to the previous screen.
Tap the "Fetch New Data" tab, and slide your finger across the switch on the "Push" tab so that it reads "ON."
Log into your MobileMe account. Click the "Apple" icon at the top of your screen and click "System Preferences" from the drop-down menu. Click the MobileMe icon, and type in your username and password, and then click the "Sign In" button.
Click the "Sync" tab. Check the box next to "Synchronize with MobileMe" and select the frequency from the drop-down menu. Check the box next to Calendars, Mail Accounts, Contacts and Bookmarks. Click the "Sync Now" button.
Sync using iTunes
Connect your iPhone to your computer. Plug the USB cable into your phone and an empty USB slot on your computer. Your phone will automatically load iTunes.
Click the device's name under the "Devices" section and click the "Info" tab. Scroll down, and check the box next to "Sync iCal calendars."
Select which calenders you wish to sync, and click the "Sync" button at the bottom of the iTunes window. Unplug your phone when iTunes shows it is safe to disconnect.