So it seems that SAR should do both.

1) First, call and leave a message if no answer. The message should contain the name of the person that instigated the search. That person presumably would be someone the hiker knows, so the hiker would infer that it is not spam.

2) Also send a text message containing the same info as in 1 above.

This doesn't require any special equipment, and since each action contains either a recording, or text message they should get through eventually (if the hiker's phone is turned off at the time, presumably the hiker will turn it on again and the messages will get through).