An external antenna is absolutely a help. Antenna gain is the same whether you are transmitting or receiving, and every 6dB of gain gives you a doubling in range.

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Assuming you do not have an after-market antenna, how would you field engineer one from wire you took from your car's electrical system? Assume the cell phone was the kind with the inch-long stub antenna sticking out the top.

Unless you know what you're doing, you could make it worse.

My thought would be to generate a text message to someone or maybe to 911 and someone else (for relay to 911) and maybe try flying the phone on a kite. Leave the cellphone antenna as is and just het the phone higher. Whenever it makes contact it should send the message. Much more reliable than a continuing conversation with a 911 operator who may not have a capability to read your position anyway.

Most Cell phones have a small rubber plug somewhere that when removed exposed an external antenna connector. My current phone had two rubber plugs so I poeed them off and one covered a screw and the other an antenna connector. I tried extending the phones antenna before and had no luck but that was before I discovered the antenna cpnnector on the side so next time I'm out of tower range I plan to try it out. The connector is very small, single strand of wire small.

A VERY interesting thought - raising the cell phone up a tree. I never thought about that.

I've heard of GMRS and Ham radio users lofting an external antenna up a tree - same thing!! Height is everything.

That was more true in the past, but is less common now. As cell phones cover more and more of the country, there is less need for an external antenna. If nobody uses the feature, the cell phone manufacturers can save a few bucks and some space by leaving the connector off. I am not saying that you can't find one. But, if you do not specifically look for that when you go shopping, you probably won't get one.

My last phone, Motorola Nextel i95c had a connector. My latest, Motorola Nextel i560, does not. I am getting a new Sprint phone in a day or two, but I doubt that it would have a connector.

Note that there are external antennas that clip onto your existing antenna, or velcro to the back of your phone. These would obviously not work great, but probably a lot better than nothing.

I was surprised that mine did, maybe because I always try to get tri-mode phones (analog support) since my parents are out where digital signals don't reach but my less than one year old camera phone has it. I checked a couple other phones at my office and they had them too.
I've noticed that there are a lot of times I'll loose signal in a valley and get it on top of the mountain so hiking to a high point could aid in getting a call or text message out in an emergency.

All this talk about cell phones has really reinforced my decision to get in to HAM. A small radio (bigger then a cellphone, but much smaller then a large police walkietalkie) can solve most of the problems people are discussing with cell phones. Under normal circumstances, cellphones are the most convienent and efficient way to use a radio. But in an emergency, either a break down of society's support system or a personal crisis in the boonies, the HAM radio gives you far more options. People are talking about attaching external antennas to cellphones. HAMs are already set up to work with external antennas. You can throw a piece of wire up in a tree and talk around the world, literally. You can use HAM radios to tie into the phone system and dial like a cell phone if you can hit someone's repeater. You can relay a message through other HAMs since emergency traffic takes priority and is one of the reasons amatuer radio exists.

I'll be taking my HAM license test after Christmas and I can tell you its probably less difficult then getting your first drivers license. There are a lot of HAMs in emergency responce groups, just look up ARES or RACES. I'm surprised more people on this board aren't HAMs. Take a look at it, HAM is a great solution to alot of these communication questions. Even compared to cellphones and to some extent PLBs, I think HAM takes the cake. PLBs are great if you are incapacitated, once you set it off it will keep calling long after you can. But with HAM, they can still triangulate your position (in fact there's a foxhunt style game HAMs play based on this) plus if you have any special needs you can report them to rescuers. It makes it real easy to say "We have someone with diabetes who needs insulin." Another benefit is that with a PLB you don't know if anyone has heard it, with a HAM radio, you can talk to your rescuers before they arrive. And that morale boost is a great benefit.

http://www.instructables.com/tag/type:instructable/?sort=RANDOM&limit=15&offset=45

The only hard part is finding a connector that will fit the cell phone antenna connector, its tiny.
If you carry a business grade laptop chances are there is a wifi antenna inside it and the connectors from it to the internal wireless card are close enough to work and usually you can get to those by just removing the keyboard.