Pick a telephone provider. Ring up their sales people, or visit their web site. Order a new phone line. Wait for ages for Openreach to get their act together and actually install the line. If you are lucky, they may actually install it on the date you're originally given.
The standard charge is around £130, provided there's a phone connection (a telephone pole or duct) nearby. It can be more (much more) if you're in the middle of nowhere and Openreach have to install a whole new run of cable.
You may get the installation fee paid by your new provider if you sign up to a package deal (e.g. phone & broadband).
