I use
www.jott.com I gotta say it's the best one out there. Nothing to install on your PPC and works with any regular phone. Best of all, it's a free service. You can set it up to send both text and email messages to whomever you specify in your jott contacts. To use it, (after you setup the account) you dial their 800 number and it asks "Who do you want to Jott" and you say the contact's name, then dictate your message. A short time later, the message is converted to text and sent out. Coolest thing I've found so far!