The deals you found seem exceptionally good, if they are still available when the device ships.

With T-mobile they are offering an 18-month contract for £29.36 per month, i.e. a total of £529 over the life of the contract. For that you get the phone, "unlimited mobile web" (which might be speed-throttled if you exceed 1GB per month), 300 SMS per month and 300 minutes per month. Maybe too good to be true.

With Vodafone they are offering a 24-month contract for £29.39 per month, i.e. a total of £706 over the life of the contract. For that you get the phone, "unlimited mobile web" (I'm not sure how unlimited Vodafone's mobile web really is), unlimited SMS and 300 minutes per month.