In case this helps anyone else, on both the Montana and the Zumo 350LM, the file on the GPS unit holding your custom POIs is called "Custom POI.gpi". If you havve no custom POIs, this file will not be present. It is created when you upload custom POIs.
- On the 350LM it is in a folder called "POI" under "Internal Storage", so /Internal Storage/POI/.
- On the Montana, the file is also called "Custom POI.gpi" but it is in a folder called "POI" under a folder called "Garmin", so /Garmin/POI/.
The filename that you need to match in order for your custom POI icon to be displayed on screen is the filename of the file that your custom POIs were uploaded from. For example, I had a file named "BMW Motorrad USA Retailers.csv", so my image file for the icon had to be named "BMW Motorrad USA Retailers.bmp" in order to be recognized as DRTBYK instructed.
Key point: Assuming the use of the Garmin poi uploader tool, set to "express" (not "manual")
you must copy your image file into the POI folder before uploading the POIs themselves. The uploading tool will take care of making the image to POI association, but if you upload your POIs before the image file is present in the POI folder, the image file will be ignored. There might be a way around that, but just stick the image file up into the POI folder first,
then upload your POIs.