Seems mobile network removed phone setting - any thoughts?

Fogmatic

Hope it's ok to post here (rather than Mobiles forum)? (I think it's about how mobile operators, well, operate (rather than the phones).

Apologies if I'm asking for advice re something that 'everybody knows', but I'm new to smartphones (though reasonably tech-savvy, including re comms, so technical language in any replies not a problem).
If I'm making a mountain out of a molehill, please tell me - that info would be welcome, too! Either way, I think there are also others it would help.

Basically, my 1st question at the moment is; did O2 remove the option to block mobile data from phones on its network?
If so, it would be interesting to know when and why (and could be useful).
The subject seems to be shrouded in mystery, but some searches on it strongly suggest that the answer's yes.
I did sort of ask in Three's forum, but only indirectly so far, and only re the particular phone that my husband's just bought (about the most basic one on the market).

I was about to get a new phone myself next, my first smartphone,. But then this subject arose with his phone, and made me wonder if I'd have the same problem or worse (if indeed there really is a problem?)
This seemed a better place than the Three forum for expertise on this kind of thing. I already have a couple of threads on the go there re other matters, with enough non sequiturs, ambiguities & other confusions to be going on with (and the mods have stated at least 2 things re his phone that turned out to be incorrect).
If any further queries are for Three, once I know a bit more I should be able to approach them with the right questions.

If this doesn't make any sense, maybe the details in the next post will help (I wanted to keep this one brief!).

Fogmatic

Just some footnotes (so to speak) to the OP.

To try & make a long story short;

When my husband's old phone died recently, I was detailed (as family tech assistant) to sort out a replacement. (We were both still using our first, basic mobiles, bought 10 years ago when the 1st signal appeared here). We're O2 users migrated to Three by the takeover, with PAYG as our only option financially.

To catch up a bit with with phone technology I read up about it the web. This included the fact that all smartphones are capable of turning off mobile data traffic. That's something we need here, because of the weak signal (and, I gather, also to avoid being charged for unwanted data when in stonger signal areas).
In the Three online shop (no stores nearby), I found the basic, back-pocket phone he wanted for just calls & texts (under Smartphones there, though it's only slightly more sophisticated than our old ones). The downloadable manual confirmed it has a 'GSM service only' setting, and we bought it.

Once I set up the phone & could see the settings, I found the GSM one was missing. I asked Doro, and the Three forum, about how to restore it, & meanwhile searched for the issue (hard to get the right keywords!). I found some some forum topics re Android phones, that seemed relevant (and some re Apple ones I think) The common link was O2, and there were remarks that it didn't occur on any other networks (I've linked below to a couple of examples). O2 as a keyword found more examples, also various problems in the Three forums that were happening only to migrated O2 users. (The usual answer seemed to be 'O2 did it, so it's not our problem', which to me just doesn't wash, but I'll cross that bridge if/when I come to it!).
Three-aka-O2 (O3?) is the only mobile network with any signal whatever in my area (which I'm in no rush to tell Three!).

Three's answer was that if he rang their Customer Services they could to 'turn off the internet' for him from their end. (This was immediately after I quoted Doro's reply saying my network would be able to help me, & the first reply I'd managed to get from Three since asking 3 days earlier). As far as we can tell, that did the trick for him.
But....

I always wished I had a smartphone while on the move, especially in London etc. I'd noticed, while choosing his phone, that PAYG Wifi smartphones had become much more affordable than I'd thought from asking around. Which was wonderful (once his phone was up & running, next stop smartphone).
But now, I'm not sure if about going ahead until I know whether other phones sold by Three Ireland (or to certain customers) are unable to turn off mobile data from the phone (and if so, which ones). Especially as it's for, well, roaming that I want a smartphone. (I believe some data gets used in the background, even when a phone's on Wifi?) I'll probably need the mobile data facility occasionally, outside Wifi hotspots. But maybe I needn't worry about it, after all?

This page of a long discussion (in the UK, I think) was the first clue for me; http://community.giffgaff.com/t5/Help-Support/No-2G-option-on-Nexus-5-only-3G-and-4G/td-p/10511333/page/11
And this Irish topic looked like another example http://community.three.ie/t5/iPhone/Cannot-turn-off-3G-for-iPhone-5-with-iOS-8/m-p/730131#M73361