Another thing worth considering is buying the phone separately and moving to a cheaper 12-month or short 1 month contract tariff.
For example, the 8GB Nexus 4 is Â£239 on Google Play. When split over 24-months, this work out at roughly Â£10/month, so if you can switch to a tariff that is over Â£10 cheaper that still covers the minutes and data you use, it would be well worth getting the phone separately.
Buying the phone separately would also mean not having to put up with the remainder of the 24 month contact if the provider does something nasty. The phone would also be SIM-free, so no cost in unlocking it either or waiting until the end of the contract for the unlock code.
Personally, I would get the Nexus 4 as my next phone but it’s not available in Ireland yet and Google will not ship here, i.e. requires UK credit card and matching UK billing address.