Wi-Fi & Other Wireless Systems
Wireless networks are another handy little addition to positioning systems, particularly the most common variety, Wi-Fi. The denser the population and development, the more Wi-Fi networks there are floating around, waiting to be utilized.
Wi-Fi networks are short-range, so there needs to be a lot of Wi-Fi networks to be at all useful for positioning purposes—and so this is only really possible in urban settings. Furthermore, to utilize this, your hybrid positioning system will require a database of all these possible Wi-Fi networks and their exact locations via their IP address to be able to triangulate position.
There has also been some limited use of WiMax technology, however, though it has a longer range than its sister technology Wi-Fi, it is also used less compared and so isn't as useful.
While this leads to arguably the most accurate positioning system available, it has very limited use. Devices that may utilize this usually require some sort of subscription fee in order to use their database as well.
Probably the best example of a hybrid positioning system that utilizes wireless technology is SkyHook Wireless.