Puppy users can phone worldwide if they have a SIp number
tmxxine, the open source time travel project (I kid you not), has released PuppySIP, which wraps the command line SIP client pjsua. Puppy Linux is one of the smallest (if not THE smallest) Linux distribution around. I use it to replace the Linux on my Asus Eee, gives me even more space.
It’s good to know that the minimal size required by pjsip clients for full SIP capability contributes to keeping Puppy Linux lean.