Hi

I've also been trying to use iaxclient from C# - see some discussion on
iaxclient-devel.  A couple of points:

1.  You don't show the delegate being created:

protected iaxc_event_callback_t CallbackDelegate;
...
// start up IAX client
iaxc_initialize(0,1); // or whatever
CallbackDelegate = new iaxc_event_callback_t(iaxc_callback);
iaxc_set_event_callback(CallbackDelegate);
...

It is important that the delegate is a member variable - if it was just
local to the code, it would get garbage collected and callbacks would fail.

2.  I found that there was a problem with the calling convention of the
callback function: .NET defaults to stdcall, but it is called as a cdecl
function.  So although it gets called once, the program then crashes.  In
.NET 2.0 you can use:

[UnmanagedFunctionPointer(CallingConvention.CDecl)]
public delegate int iaxc_event_callback_t(iaxc_event e);

but in .NET 1.1 you will need either a nasty hack:

http://www.dotnet247.com/247reference/msgs/17/87210.aspx

or add an extra C function to iaxclient.dll which has a callback declared as
stdcall.

David