Hi Lesser,
One way you can make the phone flash the MWI light is to use the IP Phone Services API to send XML directly from your application to the phone. You could use the Play URI to play files that are in the Ringlist.xml or those that are not. If the phone is equipped with an MWI light, it will be flashing while the audio file is playing, providing a visual alert as well. If you do not want an audio playing on the phone, you can create a silent audio file. When you send the silent audio file to the phone, the phone will play silence and the MWI will light up.
To learn more about IP Phone Services API visit https://developer.cisco.com/web/ipps
Here's an example:
<CiscoIPPhoneExecute>
<ExecuteItem URL="Play:alert.wav"/>
</CiscoIPPhoneExecute>
Be sure to download the IP Phone Services Application Development Notes to learn more - https://developer.cisco.com/site/collaboration/endpoints/ip-phone-services/documentation/