Firstly, please excuse my ignorance as regards the use of open source code. So, iSip (formerly SipPhone) is based on open source sip VoIP code. I want to make a similar app to iSip with some alterations in the way it works. Am I able to use the code of iSip, is it publicly available? If not, does anyone know where the open source code iSip's developers used is, so that I may build on that instead?