My 24mths expires in January and I'll be going SIM only, with BT for home phone & b/band and added a SIM only deal for my wife about 12mths ago, hers costs £12 a month (inc £5 discount) and she gets unlimited calls, unlimited texts & 6gb data.
For mine I've been paying £22pm for 1,000 minutes, unlimited texts & 3gb date, obviously I've paid for the phone (and some) but don't see the point in replacing it, so will opt for the SIM only and see what they offer, there's always a better deal elsewhere but as long as BT aren't going to spank me I don't think I'll be moving suppliers.
No doubt my phone will now begin to malfunction so as to encourage me to replace it.