PSIP (aka PuppyPhone) is a simple GTK GUI for pjsip SIP phone for Puppy Linux.
GTK version used for building: 2.18 (also works with 2.16).
pjsip version used for building: 1.10.
Other tools required: cJSON (included in tarball), and osxcart.
License: GNU GPL Version 3 or later.
Compiles into a single executable in "release" mode. Here is how to build it.
Binaries available here