We are drifting away from the sms system, but toward an interesting side subject.

I carry a PLB for most hikes I take, but not a cell phone. However, it is important to understand that a 911 call initiated through a cell phone may get a SAR team into the field more rapidly than a PLB would, because the 911 operator can make immediate, direct contact with your local sheriff's office.

If you initiate a SAR attempt by using a PLB you are contacting a communications center of the U.S. Coast Guard (located in D.C., I believe) and before initiating a search they will attempt to reach the contact person you listed with them when you registered the PLB to verify that the signal they are getting is from a place where you might be. This does involve more delays than a 911 call. The compensating benefit is that a PLB works almost anywhere there is sky overhead, while cell coverage is a gamble.