Webmail is an email service that is accessed through a web browser rather than through an application the way that mail clients such as Outlook does. Syncing webmail services with an iPhone is very easy so long as you've done the setup so that your iPhone has access to the webmail account. Note that webmail accounts include email accounts from Yahoo, Gmail, Hotmail, and AOL. Even if your particular webmail service doesn't appear on the iPhone list, you will still be able to sync it with the iPhone.
Press the "Settings" icon on your iPhone.
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Press the "Mail, Contacts, Calendars" icon in the "Settings" menu.
Press the "Add Account…" option in the "Mail, Contacts, Calendars" menu.
Press the webmail service provider from the list that appears. The list includes Microsoft Exchange, MobileMe, Gmail, Yahoo, AOL and Other. If your particular webmail service provider doesn't appear, press "Other."
Press "Add Mail Account" if you selected "Other" in the previous step. If you did not select "Other," then skip this step.
Press "Name" and type in your name, then press "return."
Type in the password for your webmail service account and then press "Return."
Type in a description for your service if you want to do so and then press "Next."
Type in the pop3 information for both the ingoing and outgoing mail. The pop3 information for a webmail account would look like this: mail.yahoo.com or mail.myweburl.com
Type in the username and password for your webmail service account and the press "Save" on the top-right corner. Your iPhone will then verify your account and sync with your webmail service.