After some research we have selected the mizutech sip webphone: [url removed, login to view] but if you can find any better then we can discuss about it. I need to integrate most of the webphone features such as auto login, transfer and conference calls.
Our crm is written in PHP and I will send the source for the selected developer.
Maybe there will be some work on the voip serve side, but its http api is also PHP based.
Well organized and commented code is a must.