A new Sim card for mobile phones is promising its users unlimited access to WhatsApp in 150 countries and across 400 network operators.

News of the WhatsApp Sim, called the WhatSim, comes as the instant messaging giant, which is owned by Facebook, announced its first foray away from smartphones, into Web-based messaging on desktop PCs and other devices.

To get the Sim card, users pay an upfront fee of €10 (or €5 in some markets). Other than that, the service is completely free for a year after purchase. There are no caps on data usage. With WhatsApp expected to launch voice dialling in its app soon, the move could be seen as another assault by so-called over-the-top companies on mobile network operators.

The Sim is likely to find particular favour among international travellers not wanting to be burnt by high roaming charges.

The WhatSim has been developed by Manuel Zanella, the founder of Zeromobile, an Italian mobile virtual network operator that offers low-cost roaming around the world.

“Anywhere in the world, it connects to the provider with the best coverage and signal right where you are,” according to a media statement.

“If you change your position, it automatically searches for a new provider. If a better one is available, it connects by itself without you even noticing it.”

The statement says Zanella had the idea for a “special version” of WhatSim “inspired by Pope Francis” that is designed for countries defined by the United Nations as the “Global South”. This includes countries in Africa.