Hi,
I have been working with Cisco VoIP since 2001 and Asterisk and freepbx ,trixbox, elastix since 2007.
what i would like to know in addition to the given info is ,
to which server are you trying to connect the Android app?
can we have access to the server side ,
there can be actully numerous issues to this problem ,
That being said I would like to have a little chat about your project to better understand the needs of the project
regards,