I don't know quite enough about the technical details to be sure, but RTK can defintiely go over IP networks with NTRIP and other protocols. The biggest limitat

I don't know quite enough about the technical details to be sure, but RTK can defintiely go over IP networks with NTRIP and other protocols. The biggest limitation with RTK is that the corrections are limited to 10-15 miles of the base/reference station (more is possible, generally with less accuracy), since ionospheric conditions vary enough to make the corrections highly location dependant. The antenna systems on RTK rovers (the devices receiving corrections, which also receive the GPS satellite signals) aren't huge, but I'm not sure if they could be reduced in size enough to fit in a smartphone.