The Cisco IOS gateway sends a burst of Frequency-Shift-Key (FSK) tones similar to the Calling Line ID (CLID) to the handset. Then, the handset turns on the Message Waiting Indicator (MWI) light and/or shows a message on its display. However, the Visual Message Waiting Indicator (VMWI) feature is not supported on all analog phones.
The Interquartz handset confirms that the VMWI feature is not currently supported. The third-party hardware vendor can be contacted for further information about the current developments.
Visual Message Waiting Indicator (VMWI) support on VG224 voice gateways
This is supported on the VG224 with IOS version 'vg224-i6s-mz.124-6.XE1.bin' using the analogue voice port SCCP endpoint feature available in this code. There is no configuration necessary to enable the VMWI operation.
The VMWI signal is passed from the router voice port to the attached telephone as a burst of FSK (frequency shift keying) modem tones that pass the MWI on and off commands. These FSK tones are only sent from the voice port when the handset is on hook. The VMWI message format is detailed here - Visual Message Waiting Indicator (VMWI)
The router voice port will also generate stutter dial tone as an in band indication of Message Waiting.Handsets that support VMWI must adhere to the specifications listed in the URL.