Accessing Yahoo's "ymail" and "rocketmail" extensions?

Maybe a year ago, Yahoo! created a new YMail extension. So if "example@yahoo.com" was taken, I could get the email "example@ymail.com". You know how the Behold is amazing in the sense that you can access a variety of emails anywhere with a signal, without the need for a data plan? And Yahoo is among those emails? Well, the phone doesn't allow access to YMail emails, even though it's technically Yahoo!. On a computer, I'd access YMail simply by going to a Yahoo! login and logging in with "example@ymail.com" as my username. Any way I can access YMail anywhere with a signal? Without a data plan?

dont know why that wouldnt work. when i goto edit account on the phone at the top it has Y!MAIL. so why wouldnt a ymail account work? think a call needs to be placed to tmo about this.