On starting a new call, the used SafeHandle might be already closed on calling GatherCallStatus. This might have happened in the GatherCallInfo method, which is called in TapiCall ctor before GatherCallStatus. In a certain case, the handle is deallocated in that method.
System.ObjectDisposedException: Safe handle has been closed
bei System.Runtime.InteropServices.SafeHandle.DangerousAddRef(Boolean& success)
bei System.StubHelpers.StubHelpers.SafeHandleAddRef(SafeHandle pHandle, Boolean& success)
bei JulMar.Atapi.Interop.NativeMethods.lineGetCallStatus(HTCALL hCall, IntPtr lpCallStatus)
bei JulMar.Atapi.TapiCall.GatherCallStatus()
bei JulMar.Atapi.TapiCall..ctor(TapiAddress addrOwner, UInt32 hCall)
bei JulMar.Atapi.TapiAddress.MakeCall(String address, Int32 countryCode, MakeCallParams param)