Customized VOIP PABX Server with software -- 2

Please see attached files for description This project required the developer to have knowledge in [login to view URL] to develop a digital PABX system from bottom up so as to integrate with the functions that i need. Essentially, it is a call center functions with some add on. Please indicate why you are confident in doing up this sytem. - knowledge in PABX, Asterisk, elastix, etc? - any example of your work? - What is the development cycle, stage and timeline?