Hi,

Just another guy asked a similar question, the problem is that you have to mod the phone to connect the electronic needed. Plus, in your case you want to detect ring only, thing that is not that easy.

One thing you could do, is to attach a strobe light with the "standard" adapter that I image is manufactured to be connected to a regular phone line) to an FXS port on router or ATA.

You would configure the user extension as shared on the analog port and IP phone, so on ring lamp will lit.

Hope this helps, please rate post if it does!