http://bitping.net can send HTTP POST, which Tropo can accept and use to launch an outbound SMS notification; pretty much any API or service that can launch a POST will work with Tropo.  This blog should help quite a bit:

http://blog.tropo.com/2012/05/23/outbound-apps-scripting-webapi/

If you get stuck anywhere on the Tropo side, just hit us up in IRC or email:

https://www.tropo.com/help

-Justin Dupree
Director of Customer Experience
Voxeo Labs