EcimDerivedString with the following pattern restriction: ([2-79][0-9][0-9])[.][0-9]{1,3}
It follows the format of "MCC.MNC". The MCC/MNC tuple uniquely identifies a mobile phone operator, with Mobile Country Code (MCC) according to ITU E.212. MCC 3 digits (200-799), (900-999), MNC 1-3 digits.