Telephone ring detect into the PLC

Does anyone have an elegant method of letting the PLC(AB5/30) know that the phone is ringing?

I'll use it to alert an operator to make their way back to the control room and attend to the telephone traffic. Probably by flashing some special lights throughout the plant which are controlled by the PLC.

http://www.smithgear.com/phone-ringers.html

http://www.vikingelectronics.com/products/search_cat_results.php?mycategory=13

Not 100% sure but if you connect a full rectifier bridge across phone line you have a dc voltage only when the phone is ringing, then use a small relay to signalize incoming call to the plc.

Thanks you guys. Mickey's suggestions lead me to some interesting sites which finally lead me to this place.

http://www.sandman.com/wizard.html#UniversalRingRelay

Looks like it runs strictly on ring voltage and provides a simple set of form C contacts for the user. Not in a case, but I can handle that.

Your help was much appreciated.

Mike