I have just posted about a technique that I have been using to send HTML-formatted emails and text messages from FileMaker without plugins.
The technique uses Mandrill, an email platform that is provided by the same team that provide the MailChimp email marketing service. Using Mandrill's API and FileMaker's "Insert from URL" script step, you can send HTML-formatted emails, attachments, and more. You can also use Mandrill to track openings, clicks, bounces, and more.
To send text messages, I've been using Mandrill and SMS gateway addresses. An SMS gateway address is simply an email address that maps to a mobile phone number. For example, to send a text message via email to a mobile phone whose number is 804-555-5555 and the carrier is AT&T, the address would be: email@example.com
I have put together a demo file that shows this technique. It's fully unlocked, and while it is very basic, I think it provides a good introduction to the technique.
The blog post and demo database are available here: http://bit.ly/1GpiwYY