I only need a private number for receiving SMS, no need for calling and sending messages. A monthly or yearly fee isn't a concern. The main purpose is to protect my own phone number from spam, unwanted promotion and data breaches. Local retailers commonly require a phone number when ordering online and some seem to only send parcel information there. Certain websites do demand a number when creating an account.
In the past I've bought prepaid plans (which expire after six months), but would prefer a streamlined approach. Preferably would support email notifications (and RSS) for arrived SMS.
My theory is that this is due to all the abuse and fraud of online disposable numbers and this is why we can't have nice things.