Please be aware that Chilli Talk have a charge (called Maintainance charge) of 10 pence per day, irrespective of whether you make a call or not. I only found out after making several calls to Customer Service to try and get my £4 credit back. I probably spent more than that in calling them. Their Terms on the website mention the fact that there may be a Maintainance charge and certainly no mention of how much.
In short, a good card to make the calls on the same day, otherwise the credit will disappear; and avoid their Customer Service if at all possible