To be clear, any data traffic through WhatsApp doesn't eat into that 200MB allowance, and better yet, the perk isn't restricted to the UK. You can also WhatsApp to your heart's content in 30 other countries at no extra cost. The roaming aspect covers the US, most of Europe and the Asian countries of Bangladesh, Singapore, Indonesia, Malaysia, the Philippines, Thailand and Vietnam.

That's what the SIM itself provides, but you can actually get 200 more minutes, 200 standard texts and 200MB of extra data each month on top of the SIM allowances simply by downloading FreedomPop's mobile apps. And since FreedomPop is a data-driven service that uses over-the-top apps to handle standard calls and texts, you've no choice but to install them. Should you exhaust all of these allowances, though, you'll then be on the hook for overage charges. Each additional megabyte costs 2 pence, but you can shell out £15 per 1GB upfront if you see yourself having a particularly active month.

If you feel like sending more money FreedomPop's way, then as always you can bolt additional features onto your plan for a couple of quid each month, such as usage alerts, visual voicemail and extra, international (virtual) numbers. Stick to WhatsApp and within your free allowances, though, and you're laughing. The new WhatsApp SIM is available now for nothing more than a £5 postage fee -- an acceptable trade, we're sure you'll agree.

This article has been edited to clarify how the current free offers can work in tandem.