Having a "real" number is very useful when dealing with institutions and companies, as opposed to regular human beings. I have had my UK virtual number from Skype for a few years now and a few times it was a life saver, because all sorts of organisations will not deal with you if you don't have a UK number on which they can call you. WhatsApp - what? Costs around 40 quid a year.
The SMS situation is a bit weird. The number they give you is a landline number. They obviously work with BT, since when someone tries to text you on that, the BT's text to speech service picks it up and calls you with a voice message, trying to read it. Better than nothing, but often hard to figure out what they want. I wish everyone switched to emails. It's 21st century, after all.