p.p.p.s. Just to make clear, this isn't going to be a good solution for everyone, it just happened to fit with what we needed.

We had already tried simplified button phones (the ones with the red, green and numbered predials) but relative couldn't get into habit of pressing green to answer. Lifting a receiver was more natural to them.

Your situation may vary, dialing may be very difficult without preset buttons, but we were mainly trying to get a phone they were able to answer!

Also, manufacturer isn't selling this as a dementia aid, just as a dial phone which works on mobile networks. (And they make old-style button phones too!)