"Mind you, perhaps the page should have checked that the phone number started 07, and rejected or queried the number otherwise"
They're not alone.
Exhibit 1. Local restaurant has (maybe had, for reasons which will become clear, I have no way of finding out) booking software which confirms the booking by text to the phone number. Some children at BT have decided that obviously landlines shouldn't be left out form the SMS fun and implemented S/W to accept an SMS, ring the landline and read out out This is a text message from $GabbledNumber $GabbledMessage
The one thing that stuck from that was "thank you for signing up to our service". It's a scam, right? After finally sorting out what it was all about - nothing more than a booking confirmation - words were said which left the distinct impression that I hadn't signed up for anything and that if they thought I had I'd better be unsigned because SMS spam is even worse when it's read out as gabble. Given that they thought this was customer service I haven't booked there since, not even by mobile.
Exhibit 2. You don't need a computer to make dumb assumptions. Our landline number is on a poster advertising SWMBO's patchwork class. The poster is in the hall where the class is held. Anyone standing there reading it should be well aware that it's a local number. So the phone rang with a text message from $GabbledNumber wanting to know if the caller should bring anything to the class. No chance of ringing back as the only contact was $Gabbled Number which has already receded into the irretrievable past. Whoever rung didn't turn up, presumably thinking that she'd been rudely ignored.
If the children at BT who'd come up with this scheme had properly tested it, including sending SMS messages to test subjects who weren't expecting the call, they might have correctly decided that it wasn't fit for purpose and should be abandoned. If they had gone ahead they should at least have supplied the originating number as CLI for the call so the recipient would have a chance of calling back to ask what the gabble was about.