cross-platform/browser plugin VoIP softphone

We require a cross-browser, cross-platform (windows/linux) VoIP softphone client that is completely integrated into the browser (like for example activeX controls for IE and Firefox Extensions). The VoIP client must be able to integrate into websites of our clients, so that customers of this client can use this application on their website. The visiting website customers are already logged in, so the VoIP application should be able to automatically fetch the identity of the user (to be used for logging into the PBX, Single-Sign On) Branding is very important, so we have to be able to make changes to the look and feel (possibly with the help of the developer). Also some settings of the VoIP client should be fixed, hidden and non-changable, such as the connecting PBX. Programming language and platform is up to the developer to decide, as long as the result is able to run in recent versions of Internet Explorer/Windows and Firefox/Windows/Linux. It does not need to be a unified solution, separate binaries are allowed. Here is a list of more detailed requirements: - The client should be webbased, so members of our customer’s website should be able to start the client from within the webbrowser. - The client should preferably use the IAX protocol, SIP when IAX is not possible - The client always needs to connect to the same VOIP server. This should be hidden into the application and not be visible in any way to the member - Our customer should be able to automatically transfer the member’s credentials into the voip client once the member starts it. Members are already logged into our customer’s website so there should be single-sign on (SSO) capabilities - Our customer should also be able to already load a telephone number into the client once the member starts it. This is convenient for letting the member automatically connect to the client's helpdesk or other services - It should be very easy for a designer to change the look&feel of the client - The client should contain a button with which the member can change some settings like the sound Input and Sound Output device that he wants to use. - The member should be able to change the volume levels of the Input and Output device - The member should be able to enter the number on a dialpad, but also by just typing it in on his keyboard - The member should be able to reload the last called number into the client - The member should be presented a Call and End Call button. - When the client starts up for the first time, it is desirable to immediately present the Sound Input & sound Output options once. These should then be saved for later use. - It would be convenient if the client contains some kind of config file which enables us and our customer to adapt settings like: o which CODECS to support o IAX/SIP with or without registration o show sound input/output settings on start: once/never/always which filters to use: Automatic Gain Control, etc...