When Family Mobile (IKEA) started up, you could have up to 5 SIM cards at £10 each, and they had a system whereby you could choose your own number if available.
I was able to obtain
xxxxxx45678 twice
xxxxxx23456 once
xxxxxx67890 once
After transferring all balances to one main FM number, I have since transferred two to GiffGaff and one to Orange with PAC's, my Orange is still on Original PAYG, so I get 5 free texts a day till 2016.
(The year, not the time !)
I just use them once every 80 days to keep them current.