I just upgraded from the 4 to the 4S today, and the next upgrade eligibility is 6/2013. I'm the primary line with AT&T, and my line is more than $100 voice and data before the FAN discount. Too bad AT&T dropped the 12 months upgrade on the primary line.
It's just not AT&T. It's sprint, Verizon. Even tmobile USA you have to wait almost 22 months even with primary line.
I just wished cell companies gave us option where u pay full price for phone in exchange for cheaper plans. But in the USA you gotta use the upgrade as soon as possible to reset your cycle cause you pay the same either way.