[wolfbln]

Thanks for your replies.
That wco81 used it in an iPad mini which is a qualified tablet instead of an iPhone which is disqualified by Orange explains why it worked properly. And it shows how ridiculous this difference is.

All over the world operators sell data-only SIM cards that have or have not voice or text. Mostly, they are a bit cheaper than the data bundles for voice cards. And in most places, you can easily use them in any GSM device for data. It's very hard for an operator to make this distinction. Normally, they just shut off voice to deter smartphone users.

1.) In the US AT&T determins the "qualified device" by its IMEI no. If the tablet or modem is not recognized as such, the plan is automatically set to voice&data. But you can call customer service and have it set to a data-only plan manually.
2.) In the UK Three tries to prevent the "misuse" of their smartphone PAYG SIM which is cheaper than their Mobile Broadband PAYG by TTL packet inspection. The internet is full of bypasses. The same is true to some tethering restrictions.
3.) Some operators may also check the mobile browser used. But they are very similar on smartphones and tablets.

If we can find out how Orange determines that a smartphone is used instead of a tablet, router or modem, we might figure out a workaround.
I don't want to question Orange's T&Cs. But according to their policy, a smartphone can't be used with their data SIM, but a mobile hotspot router (mifi) can, which can link by Wifi to the same previously banned phone. To require this intermediate just doesn't make sense to me