I've been used tropo free account as a developer for quite a time, and found it was such a great service, I am not that good at writing code but also can use Tropo with the help of my friend.
Tropo is a powerful yet simple API that adds Voice, SMS, Twitter, and IM support to the programming languages you already know.
Sign up for an account (It's Free!)
Create an application and get a phone number (also free)
Make a phone call (still free)
Send a text message (yep, still free)
Here I share my experiences about using tropo in the voice app, such as use SKYPE to call free international call: