How to read Yahoo Mail in Gmail
If the POP3 access trick described in my Yahoo Mail free POP access post does not work (and because of that the method described in this post for reading Yahoo Mail in Gmail does not work), your only option is to use a third party application.
The simplest way to read Yahoo Mail messages in your Gmail inbox is to use the free web application called Nutshellmail. Just sign up for an account, setup Gmail as your primary address and setup your yahoo account. You will start receiving your Yahoo Mail in Gmail. You can customize the hours when Nutshellmail checks for Yahoo email, but the interval cannot be less than an hour. Another disadvantage is that the messages arrive batched in a single email, but this is a small price to pay for getting the email in Gmail for free.