Virgin Media says the expansion is part of a larger "plan" to offer data-free social messaging. It's a sensible strategy, given the popularity of Facebook, Twitter and WhatsApp in the UK. The scheme does raise some questions, however, about its impact on net neutrality. Like Three, which launched "free" Netflix, Deezer and SoundCloud streaming last week, it effectively provides preferential treatment for specific services. For the consumer, it's not a problem, at least in the short term. But critics worry this type of scheme could suffocate innovative startups that offer superior services, but lack the funding to "buy in" to carrier and ISP "zero-rating" initiatives.

In the UK, the legality of zero-rating is unclear. Rules enforced by the Body of European Regulators for Electronic Communications state that such schemes will be assessed on a case-by-case basis. In the US and Canada, the situation is a little clearer, however. The Canadian Radio-television and Telecommunications Commission ruled against a "free" music streaming service offered by Videotron, given it created an "undue and unreasonable disadvantage" for services that weren't included in the plan. The FCC, meanwhile, has taken a different tack, dropping its investigations into zero-rating services offered by T-Mobile, AT&T and Verizon in the US.