The basis of accessing the phone functionality is simply through navigator.mozTelephony. Once you have a reference to that object you can start placing and recieving calls. Here are a few examples:
Telephony is currently available from the dialer and homescreen in Gaia.
Another part of core functionality in a mobile phone is sending and receiving SMS messages. Here is how to do that:
Hack and contribute
If you are interested in delving more into this and its inner workings, I recommend checking out Mozilla’s user interface for Boot to Gecko, Gaia. In there, you can take a look at the dialer.js file and the sms.js file.
And if you think using your web technology skills for developing and customizing mobile phones as well, don’t hesitate to check out and contribute to Gaia!
He regularly also blogs at http://robertnyman.com and loves to travel and meet people.