I am traveling in the US. I scheduled an appointment with some physician (no worries, I got a medical insurance). I know that sometimes patients in the US get called to confirm their appointment, but the area I am currently hiking has no phone coverage, so it's likely I cannot answer such calls. Can failure to answer such calls lead to appointment cancellation?
It might lead to cancellation of your appointment, but if you notify them in advance that you will be incommunicado then you will almost certainly be able to avoid that outcome. In other words, the cancellation should not be automatic and unavoidable.
Source: I did this once for a dental appointment.