You can normally terminate your contract but will usually have to pay the remainder of the line rental and a penalty, which was a month’s line rental when I cancelled mine a few years back.
Make sure they record the contract as settled on your credit report!
Hopefully the networks will open up SMS over GPRS/3G eventually, which is a fraction of the cost and a lot quicker.
finally got through to Vodafone customer support and they said i'd have to pay my remaining 6 months line rental (£180). which is a snip really.
As for 3G apparently (according to the gadget show) is really gonna kick off early next year with some new high tech broadband thing which will make 3G work 500x better.
they are testing it all out on the Isle of white at the mo.