my repository contains snapshots of the MjSIP releases on a branch called MjSIP-snapshots - these were created by downloading the ZIP files from the MjSIP web site
I also have a branch called sipdroid that includes the latest content from your repository under src/org/zoolu
my master branch starts from your 2.3 beta commit and it has many other fixes on it now
I've separated the MjSIP code from Sipdroid and Lumicall and placed it here:
https://github.com/opentelecoms-org/MjSIP-fork
I would suggest that Sipdroid should use this as a submodule and delete your own copy of src/org/zoolu/*
Then we can collaborate on any improvements to this low-level code.