The default Yahoo account settings under settings > email+accounts on Windows Phone does not support Contacts or Calendar syncing, so those items are not synced to a phone when the account is created… the only thing that syncs is email.
But if you also use Yahoo Contacts and Calendar, there is a workaround….which I have tested on my own (hardly ever used) yahoo account.
Syncing Yahoo Email to the Phone
To sync your Yahoo email, you’ll set up an “email only” account.
- On the phone select Settings > email+accounts.
- Tap “add an account” > select the “Yahoo! Mail” option.
- Input your Yahoo email address and password in the spaces provided. This account will sync your email to the phone.
Syncing Yahoo Contacts & Calendar to the Phone
The yahoo mail only account you created above will NOT sync any contacts or appointments that are stored in your Yahoo account to the phone. You’ll need to create another account the sync this data.