I'm currently with O2, which I'm happy with. Up for renewal/upgrade now. I think I'll end up phoning them anyway, but I don't want to sound too stupid.
I only have a little bolt-on for data, and only use my phone to access internet at home on our wi-fi. I want a data package so that when I'm out and about and want to check something on internet, it's included. What's that called?! I don't need it to be on all the time, but so that when I turn 'it' on, 'it' doesn't always go through wap and come out of my daily allowance.
Can anyone explain what I'm trying to say!?
I currently pay £15 a month, unlimited texts, a 100 minutes.

Ask them for a internet bolt on. To be on the safe side, I would go for an unlimited internet bolt on.

OP, check out Giffgaff. They are owned and run by O2 (same network). You can get 250 mins, unlimited texts and unlimited data from them for £10 a month, no contract.

I'll let you google to find their website.

I don't think O2 do them anymore. Last time I checked it was 100MB, 500MB and 1GB.

My contract was one of the last "unlimited" contracts through o2 and that was in June 10. I remember them changing them to fixed MB just after and ringing CS just to make sure I was still on unlimited it was just around the time iPhone 4 came out maybe a week before.

Thanks for your help - I went for a sim-only, £13.50, with 100MB, which the chap said should be plenty if I'm using wifi at home and 3G when out. I'm very trusting.
BUT it's on a 1 month, 30 day notice, contract, so I'll check out giffgaff and go there if this doesn't suit. Hadn't heard of them, so thanks!

GiffGaff or Tesco SIM only will be better value and both would work with a locked O2 phone and both use O2 infrastructure.

Tesco do a range of deals from about £10 a month for 500mins/500text/500MB data on a 12month contract, they sometimes do 30day contracts.