AT&T did the same thing, sounds like maybe that yahoo partnership terms have changed, and only are taking effect when the contract is getting reuped. Either pay yahoo extra cash to keep it, or revert to a diffrent level with adds, but still yahoo plus mailbox storage size.
there was a thread on her while back that the webmail interface both the "classic" and the new "beta" ones would soon be getting ads on them just like the free yahoo ones do. also the eliminated the pick 2 premium option, where u could select the yahoo plus games and such and not pay extra for it.