I've encountered this problem a couple of days ago also. Both HTC Desire's (one on Vodafone, the other O2) can't connect to the BThomehub and they've both been connecting fine with it for months before.
I used the wifi analyzer app and there's signals for BTHomehub, BTFON and BTOPENZONE being tranmitted now.....I'm pretty sure these weren't there before. The desktop computer (using a Belkin wireless adapter) and the laptops are working fine though and they're able to detect BTFON and BTOPENZONE but still connect to BTHomehub.
I've tried the usual off/on and reset fixes on hub and mobiles and also tried forgetting BTHomehub and setting up again, but it just can't get an IP address for it. The phones will connect to BTFON and BTOPENZONE....but it leads you to a page asking you to pay money!!