I just learnt something which I thought you may be interested in.
A friend came to my house and showed me her mobile phone.
It is actually her landline. Her and her husband pay Orange £10 a month and use the phone as a mobile but with a landline number.
They do not have to have BT for their internet and get that through 3 with a dongle that fixes to the wall, not one of those things that you stick in the laptop.
They were able to move home and keep their phone number as well.
I hope I have explained and you find this as interesting as I did.