The new Facetime feature in iPhone 4 is a good idea but Apple doing it completely wrong. Beside requiring both phones to be connected to WiFi (which reduce the usability by at least 50%). It also require a series of ports to be open at the firewall for the connections to works.
To put in simple terms, if you don’t understand what firewall or ports are (which I guess is like 50% of the user base) then you can forget about Facetime.
If you know what those terms means but you can’t change the WiFi firewall/router setting then you are also toasted. Most companies, education places and even hotels will puts their WiFi network behind a firewall and you basically have no way to changes the setting, thus can’t use Facetime. Because Facetime require so many open ports it is very unlikely that any admin will agree to open them up.
In the rare case you have control on both side of the networks you must open
TCP:53, 80, 443, 4080, 5223
UDP: 16399-16472
Good luck in using Facetime in real life.
