"If your lucky, some of the states offer access to the CORS network operated by the UN / NOAA / some states. the website for it is http://geodesy.noaa.gov/CORS/. I've got code somewhere that connects to it. It can work in real time if you have…"
"I did this with a pair of Hemisphere Crescent / Eclipse II receivers, and a Trimble ProXRT with all of the subscriptions at work. The 2cm is over a 5 minute time period, assuming you are in the middle of no where, and have an antenna from god, and…"