I have phoned o2 today to cancel my contract and move to BT Sim 20GB for £15 a month. It took ages to connect to o2. You must wait at least 20-30 minutes. I told them I wanna leave cancel my contract and get Pac code.
They asked why? I explained them that I found better deal with BT £15 a month and £80 Amazon Voucher.
She said to me She will price match and give me FREE Jabra Wireless headphones worth £159 or so. ( don't know if it worths that much but I found cheapest £99 online.
So if you are due to renew or can renew now give them a call and get your sim only deal for cheaper with a free headset.