Cost of Calling 0300 & 0303 Numbers from UK. Dialling 03 numbers costs no more than calling geographic (01/02) numbers, and mobiles can use inclusive minute bundles. It is also possible to call an 0300 or 0303 number from abroad.ost of Calling 0300 & 0303 Numbers from UK. Dialling 03 numbers costs no more than calling geographic (01/02) numbers, and mobiles can use inclusive minute bundles. It is also possible to call an 0300 or 0303 number from abroad.