There is no option for this. Either a dynamic icon (containing the number of missed calls) or one special icon should be used. Right now I don't know how to create such a dynamic icon. Until now all icons are pre defined fixed bitmaps.
The next questions is: How long you will see this "number on the icon"? What must happen to disappear? It is something different than typical mail applications on smartphones. An e-mail must be read to decrease the number. But I don't see any similar in PhonerLite. Opening the log book? But what happens if the log book was opened?

Are you using Windows Vista or Windows 7? There will be an overlay icon if a registration fails. See below.
If you find a small icon for such "new calls available" icon, please tell me.

Now I uploaded a new beta version. Please try that and tell me if it is enough for you.

At the risk of sounding like a idiot, the computers use PhonerLite from Sipgate.de. Is it also significantly feature-reduced version?

We had tried getting Phoner running before, but were a little confused and saw there was a pre-configured Sipgate version. When it was made clear it was similar, it was an easy choice.

By unzipping the new Phoner beta, to the \PhonerLite folder, closing PhonerLite, and starting Phoner, it uses the same configuration information as PhonerLite did, very convenient. Thank you!

There are also many more features than PhonerLite, so it's not clear exactly what was added; there are two notifications; one very useful one on the taskbar, and one bringing the application to the front. Both are very handy and we will use both. Can you tell us which one you added? 

Please make corrections if there are any mistakes in what was written.

There is no feedback from you. Is that notification icon enough for you?

Sorry, didn't understand it the last time. Nice to hear that.
I have to thank for your good suggestion and the gift.