I'm sorry for the confusion motostyle, but I just confirmed that you can send out thousands of messages a day when you subscribe to MSN Premium. Please disregard the last information that June mentioned.
Your one-week trial concern, I suggest that you get in touch with the Billing Team for this. If you're the country registered in your account is either UK or US, here are their contact numbers:
UK -- 0800-587-2920
US -- 1866 672-4551
If your country is not included above, you can contact our Billing Account Management by visiting this link: https://billing.microsoft.com