First and second users subscribe to respectively first and second mobile telecommunications services provided by first and second operator respectively. Respective user trusts the operator to perform operations in a private user domain such as a payment account. In response to first operator receiving from first user a message ordering execution of specified transaction, e.g. an SMS.message, the message is intercepted and forwarded to analysis unit. First and second operations are determined and intercepted message is amended and forwarded to second user who returns, to second operator, a response message indicating, e.g., acceptance of indicated operations. First and second operators, mutually trusted, exchange control information over a secure channel to prepare for execution of first and second operations in respective private domains. In response to second operator receiving an acceptance message from the second user, the first and second operations are executed in respective private domain. Confirmation of executed operations is sent to first and second user. Various embodiments are described including payment for merchandise.