Call barring functions should be used with care (they vary from one mobile manufacturer to the next). When blocking calls, either the user explicitly identifies authorized numbers, or they bar a range of numbers, such as international calls. This is the simplest and most widely used of all filters. Frequently the aim is to control call costs when the mobile phone is used by a third party. Subscribers can also use the same approach block data communication such as GPRS. There is a simple test that you can carry out to check that the problem relates to the SIM card: put the card into another telephone (ideally one of the same type) and check to see if call barring remains in force. If it does, then you should contact your operator to have the blocking removed.