Big Al,
Some years ago, the University of Nottingham in the UK used to sell a PC software package for about $200 (U.S.) that would capture the full signal through a Garmin GPS handheld receiver. The software would then compute an L1 solution good to sub-meter precision. Supposedly, it could do even better with the Garmin external antenna.
Of course, you had to have your Laptop connected to the Garmin while you were in the field. Apparently it did work well for some people.
Big Al,
I remember reading about that software, and being intrigued by it. Sounds like exactly the sort of thing that could be done with a smartphone now.
I think what we might see is an external antenna, you can build the gps receiver right now into the iphone but the internal antenna is always going to be problematic.
http://www.carlsonsw.com/PL_CS_SupervisorTablet.html
this already does it and it isn't much bigger than a cell phone.
Trimble outdoors App on iPhone rocks 🙂