You won't be able to upgrade this early, so your only option would be to pay an early termination fee, which is your remaining monthly payments, less the VAT and with a 2% discount. A screen repair is likely to be in the region of £150, for comparison, but it would be worth checking to see if your household or other insurance would cover it. Timpson's offer a repair service and may be competitive and possibly quicker than Vodafone or HTC.
If you do get the phone repaired, it'll be worth keeping it for as long as possible, so switch to a SIM only contract when your current one is up. I'd go for the 30-day option so that you can upgrade immediately if you want or need to. It's £2 a month more, but that's pretty cheap for what's effectively insurance.
