Im having problems setting up my yahoo account on my iphone 3gs.everytime i put in the correct details amessage comes on the screen saying...............the username or pass word for imap.apple.mail.yahoo.com is incorrrectbut i know it is correct coz i use it on my laptop hhhheeeellllpppp mmmeee

To set up a Yahoo! Mail account for sending and receiving emails in iPhone Mail:

• Tap Settings on the iPhone Home screen.
• Go to Mail, Contacts, Calendars.
• Tap Add Account... under Accounts.
• Choose Yahoo!.
• Tap your name under Name.
• Type your full Yahoo! Mail address under Address.
• Enter your Yahoo! Mail password under Password.
• Tap Next.
• Make sure Mail is ON.
• Tap Save.
• Press the Home button.

Does your new password work when you login directly via web?
If so, try deleting your account and re-enter your details on your iphone.
It might have cached your old password and hence not able to login.

Step 1: Find out which generation your iPhone is by looking at this link http://support.apple.com/kb/HT3939
Step 2: Download the correct generation with the most up-to-date number, the higher the number, the more up-to-date it is. Example: A 3GS iPhone, that would be the most up-to-date would be iPhone 3GS (4.2.1/8C148a). The 3GS tells it that it is the iPhone 3GS. The part I have put in bold, is the update number, the higher that number is, the more recent it is.
Step 3: Go into iTunes, with your iPhone plugged in, go to the left side of the screen, scroll down and select your iPod.
Step 4: The right side of your screen should now show the general iPhone information. Scroll down the screen on the right side until you see a button that says "Restore". Hold down the SHIFT KEY on your keyboard and click "Restore" on your screen. This will pop up a menu.
Step 5: From that menu, choose the update you just downloaded and hit OK. Your iPhone will now be restored. After a few minutes, you will be greeted with a welcome screen to re-sync your iPhone.
This is the only method that seems to work.

Setting up email accountsEmail account setup with Mail is easy. If you're setting up an email account for the first time on iPhone or iPod touch, simply touch the Mail icon on the Home screen. If you're adding an additional account with software version 2.0 or later, touch the Settings icon on the Home screen, select Mail, Contacts, Calendars and select Add Account.
If you're setting up a Microsoft Exchange, MobileMe, Gmail, Yahoo! or AOL account, touch the icons for those services on the Add Account screen and enter your account information. If you're setting up an email account from another provider, select Other. In software version 2.0 or later, Mail can automatically setup many popular POP and IMAP email accounts using just your email address and password.1 As Mail looks up settings that match your email account you may see a note appear that will describe any limitations you may experience in using your email account. If Mail cannot find the settings needed to setup your email account, refer to the documentation from your email provider on how to manually setup an email account.
Syncing email account settings to iPhone
You use iTunes to sync your email account setttings to iPhone or iPod touch. iTunes supports Mail on a Mac, and Microsoft Outlook (2007 or 2003) and Outlook Express on a PC. See article "Syncing iPhone " for further details.

Note: Syncing email account settings to iPhone or iPod touch copies the email account setup, not the messages themselves. Whether the messages in your inbox appear on both iPhone or iPod touch and your computer depends on the type of email account you have and how it's configured. You may need to enter your password on the device after syncing account settings.

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here is a video for doing this procedure..

http://www.youtube.com/watch?v=_Yx5yKHvfuc

Log onto Yahoo, then your Mail Account.
Near the top right hand side of the scree you will see three blued items: Your Mobile, Options and Help. Click on Options and change your preferences.
Looks compliated but it really isn't.

1. Go to "Settings" 2. Select "Mail, Contacts, Calendars" 3. Select "Add Account...." 4. Select "Yahoo! Mail" 5. Type for NAME (your user name), Address (full Yahoo email address), Password (your password), Description (do not type your yahoo email address, choose something different, like "My Yahoo Account")
The problem most likely is in the Description ... if you type your email address here, it may give the error that the server cannot connect. I changed mine to "My Account" and the server connected.
GL

if you are trying to setup the yahoo mail account as a pop3 account on your phone then you would require a premium account from yahoo and only then is it authorised from the yahoo server until then only the settings can be put on the phone

try a google account just to be sure or for that matter any other mail service which supports pop3 access

Yahoo IM is for those email accounts associated with Yahoo!, for example @att.net, sbcglobal.net or yahoo. Hotmail is associated with MSN and will not work with Yahoo IM because they are two rival companies. As far as your iPhone, Yahoo IM should work, but just to be on the safe side so you do not get charged for something that does not work, I would contact your phone provider.

Problem resolved itself. Yahoo mail must have made the necessary changes to eliminate this problem. Thanks to all who may have given this problem some thought.