Ellen,
[GeoSIM card for their cell phones*]
As surprisingly you had no response to your query I thought I would put my two cents worth. Your query on using a GeoSIM card for your cell phone was not in clear term. In this day and age those savvy enough to know of geotags and GPS are changing their cell phones to smartphones, not necessarily to an iPhone as there are more and more similar or better ( more bells and whistles) products on the highly competitive market.
Smartphones have built-in geotag and GPS capabilities so there is nothing to install: there are tens if not hundreds of location apps for the smartphones which you can download free or for a pittance if you wish to have added capabilities. SIM cards are easily available for the phones, these questions and recommendations by users have been covered comprehensively, particularly by Evan Low on this forum.
[(from the U.K.*]
The safest bet is to buy a local SIM card of the country where you will mostly use the card, an English card for UK, a Spanish card for Spain, etc. to avoid cross country charges. Most users take advantage of the proliferation of wifi (free or paid) on the Camino to reduce SIM card charges if they carry and use a smartphone.
I hope this helps and hope you can get more advise from the many helpful tech gurus on this forum
Joe