Request RSIM 10+ EE locked iPhone 6S

So my neighbour bought an iPhone 6S off his brother. Something fkin dodgy the fuckers were/are doing, but I don't care... Long story short is his brother took out a contract with O2, then sold the handset.

My neighbour is using TPO (Piggy on EE). When the new shiny phone turned up, like a dick, my neighbour puts in his TPO sim and activates the phone.

In case you don't know, new iPhones simlock (If they are on contract) to the first sim you activate the phone with, regardless of network. And thats what they stay with. So my neighbour now wants to use the O2 contract, since he is paying for it, but it wont take the SIM.

Despite many muppet ways of trying, the pair of them cant get the phone unlocked. Usual IMEI unlocks on eBay/high street have proved unsuccessful. So I suggested I could unlock it with an RSIM. Apple wont do it, network allegedly wont do it. Either way it will need connecting to iTunes to unlock anyway, and the muppet doesn't have a PC or the brains to use one...

Now the RSIM 10+ is a fairly simple process. Shove the thing in the SIM tray with the SIM card, enter the IMSI number for the network it's locked to then choose the phone type/band/unlock. Restart the phone and thats it.

That's what I think anyway. So the problem fact is that the O2 sim he wants to use actually doesn't work... I tried it in my unlocked phone and it shows no service. I went through the process and used my three SIM and it just said searching... before I lost interest and took it out. I waited a good 5 mins on each so had time to connect. Another EE sim worked fine, but it would as that's the network its locked to.

Question is about the IMSI, what is it likely to be? And what are the 'symptoms' if you use the wrong one? I also assume I should be selecting the GSM 2G/3G/4G, and not any CDMA ones?

There are a few different IMSI numbers (7 digit) for EE, T-mobile, Orange etc...

Anyone use one of these gadgets?

DJ OD