Todo integrates with other applications on your iPhone including the Address Book. When you create a task, you can optionally select a task type.

Task types include:
Normal - A standard task
Project - A task that can contain subtasks. Subtasks can have due dates/times, Priorities, and be assigned contexts and tags. Subtasks of a project effect the positioning of the Project.
Checklist - A task that can contain subtasks. Subtasks are simple and have a name and can be manually ordered.
Call a Contact - Select a contact from the Address Book, create a new contact, or enter a phone number. You'll have quick dial access from Todo when you take action on this type of task.
Email a Contact - Select a contact from the Address Book, create a new contact, or enter an email address. You'll be taken to a pre-addressed outgoing email when you take action on this type of task.
SMS a Contact - Select a contact from the Address Book, create a new contact, or enter a phone number. You'll have quick SMS access from Todo when you take action on this type of task.
Visit a Location - Select a contact from the Address Book, create a new contact, or enter an address or location. You'll be taken to the location in Google Maps when you take action on this type of task.
Visit a Website - Enter a valid website URL. Safari will be launched to that website when you take action on this task.

Task types have special icons in the task list that indicate the type of task. Normal tasks do not have a special icon. The Call John Appleseed is of type Call a Contact and has a phone icon as an indicator.

When you view a task's details, the task name has an action button next to it also indicating the task type. In the case below the phone icon is shown.

Touching the icon next to the task name will invoke the task's action. In this case, the phone numbers from the contact are displayed to place a phone call.