Yes.
Once you have decided which digital (VOIP) phone service provider you wish to use, you will need to sign a form giving them authorisation to arrange the porting of your number from your current telephone supplier -- they will typically need a copy of your latest telephone bill.
There is usually a one-off charge of £20 to £50 to complete the transfer (depending on provider) and they can typically arrange the number to be available in your home within 10 working days of your request.
Remember too that you will not pay any line rental charges.