Some good info:
http://rubicon-trail.com/Rubicon/emergency.html
In case of emergency
What to do when you need help on the Rubicon Trail
In case you need fast medical assistance due to a sudden serious illness or a vehicle accident on the Rubicon Trail you can't rely on your cell phone. Nowhere on the trail you will have reliable cell coverage to get a call out to 911 -heck they don’t even work in metropolitan areas half the time.
The most reliable method to get a helicopter in fast is to use a satellite phone. They are down to about $600 with a monthly fee of about $30 (including 30 minutes of airtime) - I carry one on all my trips. Call 911 or 530.626.4911 - it gets you the emergency dispatch for Eldorado County in Placerville - emergencies only!
The next best thing to get help fast is to use a 2 meter HAM Radio. You will have to have a license to operate a HAM radio - however, it is lawful to be unlicensed and use a HAM Radio when Life & Property is at risk. Frequency to be used on the Rubicon is 146.805 neg pl 123. The CalCord frequency is 156.075 - lets you talk to the emergency helicopter directly.
When you see the Jeep Jamboree USA helicopter (black and yellow Bell 500) in the air, you have another source for help. Trail guides and helicopter communicate on simplex 151.625 - that frequency might also reach Merlin Scott, the former caretaker at Rubicon Springs now mostly at Spider Lake. If you can reach him, he can definitely get a call out to get the paramedics to your location.
In case you have no way of communicating in any way after an emergency just run down to Rubicon Springs on foot. You'll get there faster than you think.
I am usually on the trail from Monday through Thursday and can be reached on the same frequency (151.625) - I'll be happy to call out on my sat phone to get you medical assistance fast.
If you have a CB radio (use CH 10 on the Rubicon) or GMRS family radio you might be able to raise someone on the trail to relay your call for help to the outside world. But don't count on it. CB and GMRS radios are the least reliable option when it comes to getting help.
Know your location! It is invaluable to have a GPS and be able to report your location accurately. 911 operators will have a hard time to figure out where "Walker Rock" is.