Best aproach for reacting on other software

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C#3.5

I'm asked to develop a contact management application. The main feature is interacting with their software telephone system.
This telephone system is capable of sending dos commands when the telephone rings, or when the telephone is picked up.

My application will run all day, and when the phone rings it should show previous contacts with that telephone number

I use C# 2008, and want to use one-click deployment, so command line options are not possible.

I think about a setup in which I create a batch script that first puts te calling telephone number in the clipboard, then sends a (COM) signal to my application that a call is incomming.

Is this COM approach the best way to handle this, or or do you have other suggestions ?

Thanks in advance

Rob

After the answer from db7uk I added the following information:
The make of the telephone system is Xelion, from the documentation I received there is no API.
Come to think of it, an API was mentioned once, I will ask for further documentation

Thanks db7uk for your input, other comments remain welcome!

Rob