In reply to a post by MrSaffron:

Not that I recall.

The way to do it would be to move the number to a voip service and break all the physical ties of number to location.

And even doing that, would kill the existing contract, the moment the phone number is ported to the VoIP provider, so you'd have to get the timings exactly right

i'm still not entirely convinced switching ISP now isnt the way to go? If she moves now it takes maybe 2 weeks and she can take her number with her. then she puts in an address transfer to the new property which is just round the corner in the same telephone exchange.
or am i missing something?

If new ISP is happy to do this then do it today

NOTE: 10 day notification process is 10 working days, so 2 calendar weeks minimum often migrations take 3 weeks.

Where it might get sticky is you cannot put in the move order until the migration is complete, so if you place the move order in 3.5 weeks, the move might then only take place some time after the move happens after i.e. its usual to inform a provider a couple of weeks in advance of a home move so that everything can be booked