If they really don't want to serve the UK market, then they can block +44 but given the prevalence of WhatsApp in UK and rest of the world(except for the US), I

If they really don't want to serve the UK market, then they can block +44 but given the prevalence of WhatsApp in UK and rest of the world(except for the US), I can see how people can start shipping EU SIMs to UK for WhatsApp use or create SIM SMS relay service with foreign numbers.