This seems like a really useful service in the accessibility realm. I'm not sure whether targeting "grandparents" specifically is the best move. I can see myself using a service such as this in another country, where I have bad internet connectivity. I could set up the airport to hotel connection previously and then trigger the pickup with a call once I've arrived and get the driver's details.
(Also, the popups in the lower left corner of the website with 'X recently signed up' do the opposite of inspire confidence in the service for me.)
Interestingly, the original versions of Uber accepted SMS requests, and they later discontinued it (which isn't the same as this service, which doesn't even require the texting feature, but still...).