During testing I noticed that the Telephone app for MAC OSX uses wrong codec (one a while) causing a robot voice. (a-law / u-law gets switched) Does anybody use this client? Anybody experiences this issue? Currently I suspect that its a failure in the Telephone App.
Our experience is that 'Alert-Info' is not supported by all devices, so keep that in mind. The Gigaset Pro DE310/410/700/900 even are know to fail when you send Alert-Info headers. So this solution is only Brand/Model specific.