I'm with 3.
I took great pleasure in calling them at upgrade time and asking about N900s (they didn't have them, they won't have them, and for a while, they wouldn't even work with 3 SIMs)
. And then about free super cheap phones with the contract I'm on (£5 a month for the calls/texts I use due to some discount they gave me ages ago). After making 3 or 4 calls, asking the indian sales droid awkward questions, I renewed my £5 a month contract for 12 months, and they gave me a phone which I sold for £50. The commission on that must have been pitiful.
I have the 1GB internet add on (so my total phone bill is £10 a month), which I used extensively during my 2 week stay in hospital. If the 3.5G coverage is available, you can get reasonable data transfer rates, but otherwise it is pitifully slow, and the coverage isn't always great (my new office only has O2 coverage:() What they told me when I ordered it was that there was a sort of soft cut off - you wouldn't get billed if you went above it, but that there was a limit and that they would basically cut your data connection off until your next bill period started.
I mainly use WiFi at home and at friends houses, so it's not really an issue for me.