If you haven't seen this aleady, please go and check out the following link:
Once you have signed up, you will receive an email with your personal logon details. In your new test Inbox you will see two mails, one of which will be you Outlook Voice Access instructions and telephone numbers..!
Log in, send mail, create calendar appointments and subsequently phone in to play around with OVA :) Saying "Main Menu" will always take you to the main OVA menu.
One element I would like to highlight are the languages. If you go into Options --> Regional Settings and then change the language - yes, the different English "languages" are indeed accents..!
If you change to French or German you can improve your multi-lingual skills..!