When I tried to do this a while back, the intended recipient provider (BB-NEW) told me that as a result of something that my existing provider (BB-OLD) had done they would have to give me a new land-line number.
I contacted BB-OLD for an explanation and was told:
Your services are provided through the BT Openreach network as BT own the line, we are not allowed to make any changes to the line as it has to remain compatible to all providers that also use the BT Openreach network, if there are any faults on your service it is BT Openreach that come to fix it on our behalf.
Your services are provided as an "MPF Service" this means you account is bundled so you pay only one bill for homephone and broadband, this is a common practise that was also used by your previous provider before transferring to us.
If your new provider does not have the facility to provide you an "MPF Service" this may cause them to want to install a new line, but this is not something Tesco are responsible for as the issue lies with your new provider.
As previously advised to transfer your services and number just simple make an application to a provider by providing them with your current phone number and address.
I tried again and after they accepted my order and me promised lots of sooper add-on goodies I have just been told by BB-NEW that they can't actually do it:
Unfortunately it has not been possible to transfer your current telephone number across to us and as a result we have cancelled your order. If you still want to get great value and are happy to change your number please call us.
Can someone who understands these things please explain and help me to get away from this nonsense . . . PLEASE?
I would simply move to BT except that they offer absolutely appalling value for money and seem to have woeful, unresponsive customer services.
Many thanks in advance