Yesterday I was able to cancel my contract with 3 6 months priot to expiry.
They have recently changed terms and conditions regarding the "3 like home" - which as from the 30th of June will no longer be a free service.
I recieved a text from 3 stating why the changes had been made and also that I am able to cancel my contract due to the changes.
Its a pain in the arse and took me over an hour (after being offered a good will gesture of £20) but in the end i managed to get out and only had to give 30 days notice.
If you have been abroad before and activated the roaming function , then you should be ok. I would reccomend informing them you have a trip planned in JULY and that the changes in contract will cause an increase in your billing. Which you are not willing to accept.
Def worth the hours phonecall if like me you have had problems with 3 and want out.
You can read a little more about it here
3 Like Home - 3 squirm as customers cancel contracts | BitterWallet
Cheers
Dave z