PHPList is an opensource email marketing application, it would be nice to see you integrate with that for people who self host their email lists.
Specifically, for very small businesses I would like to build and sell an appliance using your software (under appropriate licensing agreements). These would be managed and as such, I would rather self host their email lists than to add another monthly charge.
PPHList can be downloaded from the community site at phplist.org
Also, many people use Interspire Email Marketer. In a month or so, I could give you access to that if you wished to add that integration.
I am currently testing the Pro package pointed at Mailchimp for mail and Twilio for SMS.... excellent integrations!