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I want to take an analog line that is dropped on the pole at a construction site and wirelessly get it to a job trailer that is up to a few hundred feet away. They want to be able to move the trailer from time to time and not have to mess with phone wires.
I figurted I would build a wireless ethernet bridge from the pole to the trailer and convert it to back to analog dial tone at both ends. I don't want to mess with the internet.
I have done this before with analog ports on a Definity but I just installed the hardware and wiring at the remote end. I didn't do any setup.
The hardware that was used before was a Canopy wireless antenna, a small 4 port switch and a Multitech Voip device. It seemed simple enough.

Am I making this harder than it has to be?
Is there a simpler way to achieve the desired effect?
Are there any security concerns?
What hardware do you recommend?

Thank you for any input you have.

You can do it with the Multi-VoIP boxes and a good wireless router. You must be sure that the wireless equipment you get will handle the distance. A "few hundred feet" on a construction site, with a trailer that moves, may work one day, but not the next.

Where are you going to put the equipment on the pole? How will you be getting the power to the wireless/VoIP?

You will definately need directional antenna's and have to aim them at each other for anything reliable. Preferably something in the 9db+ range. You can look into waveguide antenna's (aka cantenna's) as they have been proven to work reliably in long-distance scenario's like yours. Again, they must be aimed like a gun. These are going to be 802.11b/g only (but i'm sure your not worried about a-grade service).

As far as the VoIP endpoints you could use the Grandstream 486 and 488 gateways. They are inexspensive and if this line is just for light use they will be fine. If someone is going to be on the phone all day you might want to find a more robust solution.

Just out of curiousity, why not use a 5.8ghz DECT cordless phone with a seperate charging base? I see them all the time at walmart/bestbuy/etc. Can buy a whole set-up with a base station + 3 or 4 charging stations with handsets for like $2-300.

Is there a specific reason you want to do VoIP?

Cordless phones get lost.
Using IP gives them the option of DSL to the trailer if they want it.
Inside of a 24" NEMA box I would put a UPS, WAP, Multi VoIP and a small switch(+ router if they want DSL). Directional antenna mounted on top of the box or in close proximty. The box would be mounted wherever they drop power and dial tone for the job site.
In the trailer is the same hardware except the antenna is a vehicle mount omni directional antenna. With the right antennas, range is not an issue. I would just use omnis on both ends but I don't want to create a neighborhood hot spot.
The whole setup can run off of an extension cord and everything can be packed into the box for storage or transport to the next job site.
They are also considering an IP phone system at the main office and running OPXs to the job sites. This setup would support that.

Hardware: Multi Voips, Netgear WAPs and switches,Tripp Lite UPSs and antennas from Hyperlink.

I'm not sure an Omni at the trailer would give you enough return signal strength to your base.

You can try the grandstream ATA's I mentioned earlier. They can be configured to provide just an analog extension over IP.

It sounds like you want something more robust then a single-line extension. In that case I would recommend a 4 to 6 port media gateway at the DSL modem, and use the cheaper ATA's at the trailers.

The only other thing that comes to mind is whether or not you have explained to the customer that WiFi is not secure and cannot be guaranteed to always work. I would over-stress this so you can quote it later on.

But to answer your original question:

The base/trailer box would need a media gateway/ATA, Wireless Router w/switch, UPS, Antenna.

At this point it's just a matter of piping whatever you want over it and making Box-A talk to Box-B on the WiFi.

An omnidirectional gain antenna on each end should work fine in an open environment (especially if they are mounted higher than the average vehicle that might be passing by)

The other consideration that everyone is missing.... what about the weather? You mentioned a NEMA box but that will not protect the equipment on the pole from tempurature extremes. Electronic equipment doesn't like to get too hot or cold.

Good point. As far as heat it would just have to be by trial and error. Only other thing you could do is see what the manufacturer operating spec's are on each individual piece and then compare it to the max temperature recorded in the enclosure

I've never had good luck with Omni antenna's for more then maybe 100' or so. But i've never tried using powered antenna's either.

I really appreciate all your input. Using 2 directionals may be the way to go.
As for tempurature, here in Washington we don't experience too much of the extremes. A few weeks in winter it drops below freezing (at night mostly)and a few weeks in Summer it goes over 90. Cooling is simple enough with a good fan and a temp sensor of some kind. In this environment the equipment will "probably" generate sufficient heat to keep it above freezing. There may be some kind of climate controlled box available. If you know of anything like this let me know.
I installed about 30 of these as described in my original post on a campus that needed wireless dial tone to cottages. Most of them were in carports or garages but about a half dozen had no protection at all. 3 years later they are still working. This is at a retirement facility and loss of service is life threatening. Their 911 service comes over this set up.
As for WiFi security (or lack there of), thats up to their IT guy (whom I am subbing for).

One more thing to consider is how well faxes will work with the device you purchase. Most of the construction trailers I've been in have had a fax.