If you are composing a text and wanted to send it to the people listed in your contact you can choose from the list. Here is how you can do it.
EmailAddressChooserTask emailAddress = new EmailAddressChooserTask();
emailAddress.Completed += new EventHandler<EmailResult>(emailAddress_Completed);
And to capture the email address you can have this small code.
void emailAddress_Completed(object sender, EmailResult e)
if (e.TaskResult == TaskResult.OK)