I just discovered http://Jott.com yesterday and have already started using it. Jott is currently in Beta and is absolutely FREE to use. Jott converts your voice into emails, text messages, reminders, lists and appointments. And there is a new API that compliments Jott which is called xpenser which helps you keep track of all your expenses.
After you sign up your free account just call the JOTT phone number, say the person you want to JOTT then speak your message. JOTT converts your spoken word into text and sends a text message and/or email text to the person you have in your JOTT directory. After you setup your Xpenser account you just call the JOTT phone number, say XPENSER then say (for example: GAS $42.00). JOTT is GREAT! Give it a try today.