The warning, contained in a new report by the telecoms industry analyst, comes just days after Skype announced plans for an ambitious expansion with a range of new subscription services and promises of cheaper calls.

Ovum's report states that attempting to block mobile VoIP is not a viable long-term strategy for mobile operators. Implemented well, VoIP can attract new users, reduce churn, or even encourage data plan uptake.

"Blocking VoIP is like trying to control the tides," says Steven Hartley, principal analyst at Ovum and report co-author. "Most mobile operators today have attempted different means of hindering the use of VoIP, or are cautiously monitoring usage."

At best, mobile operators offer special VoIP tariffs to avoid regulator attention, but these are not viable for end users, adds Hartley. These approaches, Hartley notes, merely garner negative publicity from vocal early adopters demanding access."

"Without outside pressure, operators would not concern themselves with VoIP until they had LTE networks," remarked Hartley. "By this time, operators would be able to offer their own VoIP services at a cost far below today's circuit-switched networks. However, in the real world, user demand, competitor strategies, and increasing regulator interest in the net neutrality debate are dictating the timeline."