Garmin,
Currently you message structure sent to SMS's are as follows:
Message inr.ch/code (lat,long) - Name.
Firstly messages cannot always be replied to (I suppose that is country dependent)
Second it is rather difficult to navigate to the point given, by a novice user (of the SMS - such as your mother in law...)
I suggest:
1. allow for a reply to be sent via the link offered. ( as SMS reply does not work for me at least. (South Africa))
2. give the option to receive the coordinates in the following format:
https://maps.google.com/maps?q=latlong
example: https://maps.google.com/maps?q=-25.834123+28.123123
on an android phone you can simply tap on the link and hit navigate or Start and the phone will direct you there.
There is a android app "Here I Am" that sends a position in that format that I've been using for years flying hang gliders
Thanks
Tobie