Emergency CB Radios: Lots of folk carry an Epirb. Some (like me) carry a Satellite Phone. Big bucks when your life/safety are the issue. If you are on a budget you might consider a Dual-band CB radio such as the Baofeng which can be bought for less than A$50 including a battery pack which takes 6 x AAs – in addition to its lithium battery (or you might power/charge it with something else you already carry). Around 200 grams, I know but you get (receive only) FM radio (For weather forecasts etc), a UHF radio with duplex which can access the Channel 5 emergency frequency (you can be pretty sure someone will be listening anywhere in Victoria at least – http://uhfcb.com.au/40-Channel-UHF-Infomation.php), and HF (ham radio) as well (for which you should have a licence) but which propagates wonderfully from more remote locations. It would be a good tool also for keeping in touch with other users on the trail. You can also buy a higher gain antenna for a few dollars more. A car kit is also available. For example: http://www.amazon.com/BaoFeng-UV-5R-Dual-Radio-Black/dp/B007H4VT7A or http://www.ebay.com/itm/BAOFENG-UV-5R-CTCSS-Dual-Band-Radio-Walkie-Talkies-Original-AA-Battery-Case-pack-/391219854780?hash=item5b16853dbc
Note: You need less signal to send an SMS than a voice call: This may get a message out when other means will not.