Creating voicemail heatmaps using ringless voicemails is not a common or typical use case for ringless voicemail technology. Ringless voicemails are often used for marketing, outreach, and communication purposes, but not for generating heatmaps. Heatmaps are usually associated with data visualization and analytics, often used to represent data on a geographical map or a visual grid.
If you have a specific project or use case in mind for creating voicemail heatmaps using ringless voicemails, you would need to outline your goals and objectives clearly and then consider how you might collect and analyze data in a way that could be represented as a heatmap.