WHAT ARE THE BEST PLACES TO INSTALL WI-FI /VOIP/SECURITY CAMERAS?

It all depends on what your trying to accomplish with the security cameras.
WIFI (802.11″X”) “hot spots” are virtually in every city, industrial area, major hotels, coffee shops, airports, etc. Momentum is building for the various applications that take advantage of the bandwidth and “anywhere, anytime” connectivity that Wi-Fi delivers. While wireless access to laptop’s is still the major use of WIFI, there are dozens of other applications where this technology is being used.
You can install a security camera almost anywhere using WIFI that offers high-speed access. Many of today’s CCTV manufacturers already offer various forms of cameras that can utilize this technology. In Los Angeles, there are hundreds of CCTV cameras over the freeways bringing real-time video to news stations who report on traffic conditions. The CCTV camera is equipped with a PCMCIA slot where a wirelss card is inserted. The receiver is located a few hundred feet away and transmits the video back to the station.
VOIP is exploding in the Internet Phone Services market. You can use VOIP virtually anywhere WIFI exsists. In the security market, you need to be careful about recording any audio as many states make it legal to record video in public places, but illegal to record audio without sufficient signage and public awareness.
As for your question of “where is it most needed”, the answer is everywhere (bandwith allowed). However, the market is not 100% ready for it yet. The CCTV market is still actively trying to switch over all security/surveillance customers from analog tape recorders to digital video recorders. The IP market is where many of today’s manufacturers have arrived, but have to remain patient until the market can accept it.