I remembered from my G1 days a way to sync the E-Mail app up to Yahoo's free (not PoP3) servers so I gave it try on my new BH2 and it works just fine:
Here are the steps:
1. Enter Yahoo ID and Password (hint, just use your "username", not the whole joeblow@yahoo.com
2. Select Manual Setup
3. Setup IMAP
4. Incoming server is imap.mail.yahoo.com
5. Port is 143
6. Security Type is "TLS (if available)"
7. Leave IMAP path prefix blank
8. Hit next
9. SMTP Server is smtp.mobile.mail.yahoo.com
10. Port is 25
11. Security is again TLS (if available)
12. Check Require sign-in
13. Verify username and password
14. enjoy
To Sync up, you CANNOT be on WiFi (dunno why, maybe Yahoo has a deal with T-Mobile?).
One other note: if after rechecking all your settings and it still says "invalid username/password" try going onto your Yahoo Account and change your "Location" to ASIA ! Weird I know, but for some reason, some people can't get this to work with US-English as their Yahoo Locale (not talking about your phone's settings here, all on Yahoo site end!).
Here are the steps:
1. Enter Yahoo ID and Password (hint, just use your "username", not the whole joeblow@yahoo.com
2. Select Manual Setup
3. Setup IMAP
4. Incoming server is imap.mail.yahoo.com
5. Port is 143
6. Security Type is "TLS (if available)"
7. Leave IMAP path prefix blank
8. Hit next
9. SMTP Server is smtp.mobile.mail.yahoo.com
10. Port is 25
11. Security is again TLS (if available)
12. Check Require sign-in
13. Verify username and password
14. enjoy

To Sync up, you CANNOT be on WiFi (dunno why, maybe Yahoo has a deal with T-Mobile?).
One other note: if after rechecking all your settings and it still says "invalid username/password" try going onto your Yahoo Account and change your "Location" to ASIA ! Weird I know, but for some reason, some people can't get this to work with US-English as their Yahoo Locale (not talking about your phone's settings here, all on Yahoo site end!).