My own view was initially that if the (0115) number exists and my BT phone won't call it, but an NTL line WILL, then I'm being deprived of a phone service and if BT won't fix it I'll go to Ofcom.
Having spoken to NTL, BT, O2, Ofcom and Otelo, I'm getting the feeling that the 0115 0xx xxxx number, despite looking like a geographic number but isn't (because of the zero) IS permitted under Ofcom rules; Further it should NOT actually be diallable from ANY phone line, and so the fact that you can call it from an NTL line is a bonus.
Although (as someone else previously commented) if you try to dial 0115 005 xxxx from within Nottingham and decide (quite reasonably) to drop the 0115, and just dial 005 xxxx, in my daughter's case you start to dial a Belize number (international code 00 501) - given that I only dial three more digits after, there are probably insufficient digits to actually make a call, but even so, it sounds like a bodge to me!
However, it seems that there's not much we can do, so long as Ofcom continues to allow numbers which look geographic, but aren't really.
Suggest, if you're interested, you take it up with Ofcom and Otelo - you might have more success than me.
There's new info on Ofcom's website about this
http://www.ofcom.org.uk/telecoms/ioi/numbers/numbers_administered/#geog1It's in Excel format and takes ages to download, so be patient.
There's a glimmer of hope .... the number range which I'm interested in are designated "free for national dialling". They described the number format as:
(0)+10, which I think means:
(0)11500x0000
as opposed to conventional geographic numbers which are described as:
3+7, which I think means
(0)115_xxxxxx
i.e. in our case it is NOT seven digit Nottingham number preceded by (0)115, but it's a ten digit number which happens to start (0)115 and which happens to relate to Nottingham exchange.
Let me know how you get on
Notty