A smart card associated with a subscription to a first telecommunication network and coupled with a communication is personalized by an application server. The server receives a request of subscription change having an identifier of a second telecommunication network; establishes a secured session with home location register of the second telecommunication network identified by the identifier and receives a first message having a second international identity and a second authentication key from the home location register; and then sends a second message having a personalization command, an admin code, the second international identity and the second authentication key to the communication device. The smart card is able to interpret the personalization command to delete the first international identity and the first authentication key and replace them by the second international identity and the second authentication key if the admin code is valid.