OK, I just went to the website and upgraded my service. Two things though. First, it still isn't working but probably not enough time has passed. Second, the confirmation says this:
The Windows Live Hotmail Plus yearly subscription of $19.95 plus tax includes 10 Gigabytes of total Windows Live Hotmail account space, the ability to send larger attachments, and exemption from the account expiration policy.
But, before you buy the service, it also says this:
Bigger distribution lists. Send e-mails to a much larger group of recipients than with regular Hotmail.
I just want to be sure that an ability to send emails to more than 250 people within the same day is an option included in this upgraded service.