Help with iphone 4

Son wants to buy an iphone 4 (cant afford to get a phone on £25 contract so iphone 4 is his limit). Can get a refurb one from The Deal Channel on TV for £240. Figure its better than paying £180-£220 on ebay as we get 12 months warranty. Problem is the network. I want to put an O2 simcard in as it is PAYG with balance of £90+.
Advert says it is on EE/Orange/Tmobile. However, i don't know how this could be. I was speaking to livehelp on Tmobile website and he says a Tmobile phone will not work with an orange sim and vice versa so it is not possible to have a phone that will work on either (unless unlocked). Two different people told me that although they share the same netwoek signal the simcards will not work in eachothers phones.

does anyone konw if this is correct, and how they could sell a phone as working on all EE/Tmobile/Orange, or whether it is probably unlocked

Both Orange/Tmobile will only unlock an iphone after 3 months, so we would have to go on one of those before switching to O2

Or does anyone know anyway selling Iphone 4s with warranty etc for around £200

TIA

 

Iphone 4 / DYSON ?

Yeah. that £6.90 contract is similar to what he is paying £10 a month on O2 PAYG, only difference is on the PAYG unused credit rolls forward (currently £94 cos he doesnt speak to people - just sends texts!). Was either going to go with 3 or stick with O2. Never understood how 3 can be so much cheaper than others - is there anything wrong with them?

livechat guy on tmobile told me about the not being able to use phones locked to orange and vice versa, although an orange will work and orange and EE, and Tmobile will work on Tmobile & EE. So i cant understand how a phone can be sold as being on the EE/Tmobile/Orange network - surely it cant work on all of them, but not other networks

DYSON - weren't you something to do with EE. do you know the answer?