Asterisk w/ CO VM & MWI

I have a Cisco 2611 router with both FXS and FXO cards in it. The PSTN POTS line is connected to the FXO port. All my home phones are connected to an FXS port. I also have a couple of Cisco 7940 IP phones that I converted to SIP. I want to use the Asterisk server to pass all my International calls through a SIP provider. When the wife picks up an analog phone and begins to dial an International number, the Cisco router would route that to the Asterisk server, which would then route it to the SIP provider.

The issue I am having is with the phone company’s voicemail service. When someone leaves a VM, all our analog phone detect this and a Message Waiting Indicator (MWI) light begins to flash. How can I continue to get this functionality with all my phones plugged into the FXS port on the Cisco router and my SIP phones connected to Asterisk?