Asterisk Specialist needed

Hello freelancers, We are a Sydney and Melbourne based Photography Studio and are looking for a Person to help us with our Asterisk PBX server and everything connected to it. For PBX we run a Virtual Box with Linux Ubuntu and Asterisk as Telephony System. Host OS for this is Windows 7. In our call centre we have currently 12-15 Lines running, all using JITSI Softphones and Jabra USB Headsets to make outgoing calls. Outgoing numbers are set to mobile numbers, so clients call back each booker on their individual mobile phones. This all is based in our Sydney office. We are looking for somebody to help us with this system, to fix some problems we have, maintain it, improve stability and extend eventually. Our main Issues are that the System is not running stable, we have trouble with JITSI not being able to Phone out sometimes, lines being too noisy, poor speech quality and several other problems. Also, after finding a solution for the above mentioned problems, we have several more office phones, that run via on Linksys SIP boxes and a several VoIP Provider, that we may want to run via Asterisk. Also beneficial would be to get our offices connected via Asterisk, to be able to make the cheapest possible calls between them. In order for this to work properly, we want to get our current problems resolved first. This can be done remotely, we provide VPN and RDP access to the required servers. We would like to find a suitable person, figure out a how much work and what kind of work is necessary, and then find a suitable price for the project/s. Thank you, The Photo Studio Michael Wetterauer