Not true! I have Yahoo set up on my HTC Droid Eris. You have to set it up as Imap and make sure your WiFi is turned off. I then have it set to search every 4 hours for mail. I have not had any problems.
Caution: Before Proceeding, ensure that WIFI is turned OFF. This only works via Verizon 3G Signal.
Go to Mail icon: You will be prompt to enter in a username and password. Enter in your Yahoo email
Click on the Manual Setup at the bottom left corner
In the incoming server setting, entering as followed
username:
xxx@yahoo.com (enter in your complete yahoo email address)
password: enter in your yahoo password account
IMAP Server: imap.mail.yahoo.com
Port: 143
Security Type: None
IMAP Path Prefix: leave blank / Optional
Press next to continue with SMTP Server. Once on that screen, enter in these settings
SMTP: smtp.mobile.mail.yahoo.com
Port: 587
Security Type: None
Check "required Sign-In"
Username:
xxx@yahoo.com
Password: your email password
Now click through next and fill out the name, etc. You are done