PhoneVite

Totally free and easy-to-use event/party planning suite for your mobile. PhoneVite lets you send free voicemails (i.e. party invitation, group meetings) to a group of people and follow-up on their replies. Simply record your message/invitation (from Phone or PC ) and Phonevite will instantly deliver it to phone numbers of your contacts. All recipients have and option to reply without being charged.

Features:

Record and Send your invites/announcements over the phone
Send voice messages to several people simultaneously
Record voice messages from PC or Phone
Very good call quality
Import contacts from: Microsoft Outlook, YahooMail or Gmail
Organize contacts into groups and send voice messages to particular group members
Get responses: Recipients have an option to answer using 1 (for yes), 2( for no) or 3 (for not sure) buttons. OR leave you a full voice message.
Call Tracking: Keep track of all the calls and responses for your events.
View Demo tour: http://www.phonevite.com/help/screencast/