I have found something on that page
Unlimited BT Infinity 3 + Calls
£37.25 until 01/12/2014. For new BT Broadband customers only that sign up for an 18 month minimum term and pay BT line rental – see standard line rental note for prices. Includes Unlimited BT Infinity 3, Unlimited Evening and Weekend Calls and a BT Home Hub 5 (unless BT has already provided you with a Hub).You'll need to pay by Direct Debit and there's a £6.95 delivery charge for the Hub. Subject to availability, minimum line speed and computer specification. Terms apply.
Unlimited BT Infinity 4 + Calls
For new BT Broadband customers only that sign up for an 18 month minimum term and pay BT line rental – see standard line rental note for prices. Includes Unlimited BT Infinity 4, Evening and Weekend Calls and a BT Home Hub 5 (unless BT has already provided you with a Hub).You'll need to pay by Direct Debit and there's a £6.95 delivery charge for the Hub. Subject to availability, minimum line speed and computer specification. Terms apply.
(Scroll down and click "packages")
No price/details for infinity4
Ian