Google Calendar is an online calendaring tool that offers many advantages such offline calendaring (using Gears); You can enter events as free text, with keyboard shortcut “q” or click the “Quick Add” link in the upper right-hand side of the page. Then enter your event: time and title are the bare minimum..
For Gmail users, you can add event within Gmail that can recognize event-related information. If it finds some, it will give you an option to add it to your calendar. Simply click on the link and you can edit the event and send it right to your calendar…
Starting iPhone OS 3.0, Apple introduced new feature to sync bi-directional OTA (over the air) with CalDAV. Both Google calendar and Yahoo Calendar Beta (if it is available to you) support CalDAV. Syncing calendar to your iPhone can be done without plugging into your computer.
On your iPhone, go to settings.
Tap "Mail, Contacts, Calendars".
Tap "Add Account".
Tap "Other" and then tap "Add CalDAV Account".
For the "Server" you can simply type "yahoo" (or :”Google.com”
Now type in the Yahoo! username and password (Gmail address and password)
Once you click save, the iPhone will verify your username and password.
Next time you open up your iPhone Calendar you will see a page allowing you to select with Yahoo! Calendar or Google layer you want to view/edit.