If you are a UK traveller looking for a SIM suitable for international travel, I strongly advise that you avoid WorldSIM at all costs.
Firstly, the 'free UK mobile number' that they advertise, is not. The number allocated is actually an Isle of Man, Manx Telecom number. IoM is not part of the UK, and therefore any calls to this number are not included in any inclusive minutes. Depending on operator, calls to the IoM number are charged at 50p/min on average.
So in the first instance you have false advertising...
Furthermore, this SIM cannot receive calls from another (UK) mobile number, only landline. The company claim that as it is an international SIM, it needs credit to call it, but that doesn't make much sense. So, secondly, what use is a phone number if noone can call it from another mobile?
In seeking assistance, customer service is poor. Little to no understanding of the product, and particularly the difference between IoM and UK assigned numbers. Written enquiries are seldom answered. Enquiries raised by phone have something like over a 10 working day response time.
In finally being promised a refund on returning the unworkable SIM, this has not been honoured. Companies like this thrive on customers getting fed up trying to claim rather than doing the right thing, and providing the service their glossy websites imply.