The latest BT agent I spoke to about this was, typically, unable to clarify exactly which numbers are covered by the bar, but encouraged me to make some test calls and inform them of any unwanted charges. So, I cautiously began dialling an 0901 number. To my surprise, the call disconnected when I dialled the fourth digit after the 0901 prefix (the 'call disconnected' tone sounding for exactly one minute). I then dialled an 0902 number and the same happened. I worked my way through 0844, 0845, 0870, 0871, 0872 and 118. Of all the examples I tried, only 0871 numbers similarly disconnected (following the third digit after the 0871 code - not the fourth as with 09 numbers, for some reason). All the other calling codes I tried allowed me to dial to the penultimate digit of the number. I then, obviously, hung up before risking a charge (though 0845 and 0870 are, of course, inclusive with BT and I didn't really expect them to be barred).
I can't find any 0842, 0843 or 0873 numbers to try (do they even exist?), but I'll be willing to bet they're not covered by the bar either.
To summarise: BT's 'International and Premium Rate Call Barring' feature only appears to bar calls to 0871 and 09 numbers. Plus international numbers, of course (calls to the latter disconnecting after one has dialled the country code or a few digits thereafter). That's pretty poor for a feature normally charged at £1.85 a month. I suppose it's possible that the exact numbers covered vary by exchange and perhaps that's why BT keep quiet about it. Another theory is that 0871 and 09 are long-established codes (dating from the late 90s/early 00s) and BT simply haven't got round to updating the call barring technology at their exchanges to cover the newer 0872, 0873 and 118 numbers - all of which are defined as 'premium rate services' by Ofcom, presumably because they are all regulated by the Phone Standards Authority (along with those strange 070 numbers). 084 numbers are outside the PSA's remit and it's therefore, I suppose, a bit of a 'stretch' to expect them to be covered by such call barring features.
It's frustrating that so much confusion continues to abound over the term 'premium rate'. Even Ofcom are vague on the matter, saying that such services "usually operate on numbers beginning 09, 118, 087 or five or six digit mobile voice and text shortcodes". "Usually" isn't good enough. The Government website has a useful table of UK telephone numbers, clearly showing those which are PSA-regulated, but even that only uses the term 'premium rate' to define 09 numbers specifically. My wish is for all four PSA categories to be officially classified as 'premium rate', according to different charge bands: the lowest (i.e. cheapest) being 0871 numbers (PR1), with 118 numbers the highest (PR4). That would be too simple, right?
Links:
https://www.ofcom.org.uk/phones-telecoms-and-internet/information-for-industry/p...https://www.gov.uk/call-charges