How smart do you have to be to buy a $100 GPS receiver from Wal-mart?
That said, they don't have the technology to truly use GPS as a guidance system. It only tells you where you are.
Like ships, transoceanic pilots had long stretches of absolutely no radio communication. If the airliner went down, often we never found out where or why. They used mostly, and sometimes only, ded reckoning, short for deduced reckoning, using only a compass, airspeed indicator, and clock. This is accurate if the math is done carefully, though winds aloft can push the airplane hundreds of miles off course. At night they could use celestial navigation to check their positions the same as ships. Radio automatic direction finding to islands was used but required someone on the ground. Later they could sometimes use Loran, which stands for long range navigation, somewhat similar to GPS but the transmitters are ground based, a few on small deserted islands, using large amounts of power. Many Loran stations are still operating. Expensive inertial guidance systems were developed and are still used but these become inaccurate over time. This is what JAL 007 was using when they strayed into Soviet airspace and got shot down, though due to a pilot programming error. Ships use these same technologies but also increasing rely on GPS. What makes most of the world nervous is that the US pays for and controls the GPS satellites. The Europeans and other countries are trying to develop their own systems because of this.
Airliners never use VFR once they reach controlled airspace. They are assigned IFR airspeeds, altitudes, and headings, and must fly specific highway in the sky routes. GPS will enable airlines to get off the airways, making for direct routes and added traffic capacity, but this requires new computer systems on the ground to coordinate everything.