Is your current ‘existing BT landline ‘ a working line with a BT number ?, if so , and it’s possible to do what you want ( renumber an existing BT number , to a number that is working with another provider that is already ported from a third company,) I can only see problems, the first being getting someone to say ‘it’s possible’ rather than just saying ‘No’.
In effect your ‘order’ would need to stop your existing number ( without ceasing the broadband associated with it ) and renumber it to a number with a VOIP provider...I’m not sure that type of order even exists , if it does, then it would require the VOIP provider not to return the number to Virgin when your VOIP service is ceased ( obviously if you served ‘notice’ to the VOIP provider that you were leaving that’s what would happen , the gaining provider would have to serve your notice ) then it gets opaque, do Virgin port direct to BT, or do Virgin continue to port to VOIP and they ‘re-port’ to BT , porting a ported number has never been ( to me at least ) explained.
There has been some chat on this or similar forums from consumers who want to move a phone number to a VOIP provider without ceasing their broadband service that the phone number hosted, it was stated that a ‘stop, port and start renumber‘ order was available from BT Wholesale to supposedly arrange that, but the person asking the question ( AFAIK) never commented on if they ever got what they wanted without losing broadband for a while....your case is IMHO even more complicated.
Number port as never designed to be ‘it’s my number and I can move it where I like’ , the fact is it was initially designed when there were only really two options , BT and the regional cable company, the arrangement was reciprocal, if you wanted to import numbers ( this was massively to the cable company’s benefit ) you had to export too, but initially at least , the vast majority were from BT to cable, adding in technological advances like VOIP providers as well as the more traditional networks , and the many many providers that now exist it’s not surprising that the initial concept struggles to keep up with customer expectations, you may be expecting too much from the system, and even if the system has this set of circumstances covered, getting an agent to recognise it, and 3 company’s to coordinate, when one has no relationship with you, and another is about to have no relationship with you.
