Someone told me the non-geo number would show up on their phone's display regularly when called from their work phone. Apparently the number they originally dialed would first display, as normal, then simply change to the non-geo number at some point before the call was connected - not sure if this was before it started ringing or after, sorry.
This was at a large financial organisation, which unfortunetly they no longer work for, so no chance of getting them to "convert" some numbers, sorry!
Makes you wonder if they had a system (unoffical or otherwise) which always attempted to route non-geo numbers via the geo number, when this proved to be more cost effective. I guess this could all be part of a complex least-cost-routing system whereby 0845 numbers may be charged at a higher rate than a standard local number due to arrangements they may have with telco's on call volume or whatever.
IIRC, a number of "alternative" telco's, such as onetel and 'telco' do in fact charge a higher rate for 0845 than for a standard local call, at least via their freephone (0800) access numbers (eg. calling cards and/or "walk 'n' talk") but not via calls routed to them via a BT line using their short code prefixes (eg. 1696, 1877 etc)
Sorry if I went on a bit, especially on my first post, hopefully someone reading found it remotely interesting