Question: I've already read [this](https://outdoors.stackexchange.com/questions/5446/what-specific-features-should-i-take-into-account-when-buying-gps-device-for-geo) and [this](https://outdoors.stackexchange.com/questions/4045/how-to-select-a-good-gps-receiver) to get some background knowledge on GPS tools, but I'm still left with some questions:

1. Is there any way I can get a device that consistently provides accuracy to within 10 feet in less than a minute or two?
2. I've messed around with several iPhone apps, but haven't had very good luck thus far. What's the most accurate a phone can be?
3. If I can't have accuracy to less than 10 feet within two minutes, what's the closest I can get to that goal? (Both in terms of time and accuracy)

I only need to be able to accurately determine the coordinates of specific locations, so I don't need any additional features--even poor battery life isn't a big deal.

Answer: 
1. No. GPS is not autonomous. Errors in satellite vehicles can and have propagated to ground stations (I have one on record from a working GPS receiver placing me kilometers from my actual location that coincided with a published failed software update in the satellites). Additionally, selective availability, while not likely, can be turned on by DoD any time it likes. Because there are so many thing to go wrong, it's not possible to use GPS in systems that have a hard performance requirement.
2. Iphone (like all cell phones) has a small GPS antenna and the GPS is akin to "would you like fries with that". i.e. GPS is an add on rather than its reason for existing, and is inferior in nearly every way to a dedicated GPS unit. .
3. Can't say. GPS results are statistical, not hard and fast. Study standard deviations and such like to get an idea of how to specify required GPS performance. After that, I am sure money comes into it, and for the right amount, you can get what you are after, but only as long as you can specify it.

You may be interested in studying up on "Receiver autonomous integrity monitoring" (RAIM) as well. 

If you can't be bothered with all the above and want a simple answer - buy a dedicated GPS with the smallest TTFF (Cold start, non assisted) you can afford. This is as good a guide to sensitivity and quality as you will get without becoming a rocket scientist.
Over a small area you may be able to do something. I don't know if you have a small area to deal with, and 10ft might be pushing it even then. Basically you fix the position of a known point by some means (it might not even have to be fixed absolutely depending on your goal). *Long term* GPS averaging might do that for you. Then you use this known value to calibrate an offset. You'd need a laptop connected to a dedicated GPS unit and probably custom code. If you could also access differential GPS signals you'd need a beacon receiver for that, but wouldn't need the known point or your own code. 

But over a sufficiently small area compass triangulation can get surprisingly good *relative* accuracy; once again you need well-surveyed references (and line of sight to them).