As part of the September 2012 release, Marketo exposed the ability to create a Webhook. Webhooks are essentially HTTP callbacks that allow you to send a "payload" (i.e. xml, json) to a URL and include parameters.
Here is a walk-through on how to create a Webhook that sends an SMS Message to a Marketo Lead using the Twilio messaging platform.
Select Treasure Chest from the left tree and click Edit in the Webhooks section
Check the box to Enable Webhooks
In the Admin menu, select Webhook and click New Webhook
Enter the Webhook details as defined in the below screenshot. A powerful feature of Webhooks is that you can include Tokens as part of the URL and/or Message for further customization.
Note: You will replace the [ACCOUNT_SID] & [AUTH_TOKEN] values with what is specified in your Twilio account.
Create a Program/Campaign in Marketo. In the example below, a Program/Campaign was created with associated LandingPage/Form to send out an SMS text message when the lead fills out form.
See the activity appear in the Activity Tab for that lead in Marketo
Check SMS activity in your Twilio Account Log