Methods and apparatus for improving caller identification in telecommunications services based on general-purpose networks are described. A gateway device may process invitation messages sent from a telephone via a private branch exchange, in which the private branch exchange has replaced the number of the telephone with a customized number. The gateway device may determine that the customized number is mapped to an account-related number, and insert that number into a field of the invitation messages that is examined by a telecommunications provider and associated trunking services for account-related purposes.