Misses the point...
I use my mobile phone a fair bit for my business, the number is on my business cards and clients are invited to give me a call anytime. I get at least 3-4 spam calls a day from other companies wanting to sell me their services, completely ignoring my TPS entry for this phone.
The former I'd grudgingly pay for, the latter I'd strongly object to paying for. If someone wants to dial a mobile phone number to spam me services then they should foot every penny of the cost.
Also "people increasingly want one phone number that never changes". Do they? A mobile number is very distinctive and sets people up to accept the mindset that they are calling a less reliable technology than wired lines, may get cut off unexpectedly or catch someone in a hurry who might be a bit more abrupt in giving a "call you back later, on the train" then cutting you off.
I use Skype regularly for calling friends, my wife does as well, this has NEVER resulted in me coming close to my broadband usage cap. The bandwidth used is effectively so trivial compared to my cap that it is free for all intents and purposes.
Enough of the rubbish. Keep it as it is, if someone wants to call me, let them pay the cost of the call; if they don't want to pay, no-one is forcing them to call. Conversely, why should I have to pay to find out if I want to speak to whoever is calling me?