Method for verifying the validity of a telephone line of a user likely to use a service or a software application, with the purpose of authorising said user to use a service or a software application, by means of a communication terminal of the user associated with said telephone line, the method comprising: - the initiation (E1, E2), by a client system associated with the service or with the software application, of a validation procedure of the user likely to use the service or the software application, said validation procedure being associated with an ID of said user and with said service or with said software application, the method being characterised in that it furthermore comprises the following steps: - the allocation to said validation procedure, by a validation system, of a temporary validation telephone number having a predetermined validity duration, - the generation of a call by the communication terminal of the user, via a telephone communication network, to the temporary validation telephone number, - the reception of the call by a call server, - the transmission of the call received by the call server to the validation system, - the notification by the validation system to the client system, where applicable, of the call received intended for the temporary validation telephone number, during the predetermined validity duration of said temporary validation telephone number, - the verification of the correspondence between the temporary validation telephone number called and the validation procedure, to ensure that the communication terminal of the user emitted the call intended for the temporary validation telephone number, during the predetermined validity duration of said temporary validation telephone number, and - the validation of the telephone line of the user insofar as the correspondence between the temporary validation telephone number called by the communication terminal of the user and the validation procedure has been verified in the preceding step, such that the client system is able to authorise the user to use the service or software application. - the initiation (E1, E2), by a client system associated with the service or with the software application, of a validation procedure of the user likely to use the service or the software application, said validation procedure being associated with an ID of said user and with said service or with said software application, - the allocation to said validation procedure, by a validation system, of a temporary validation telephone number having a predetermined validity duration, - the generation of a call by the communication terminal of the user, via a telephone communication network, to the temporary validation telephone number, - the reception of the call by a call server, - the transmission of the call received by the call server to the validation system, - the notification by the validation system to the client system, where applicable, of the call received intended for the temporary validation telephone number, during the predetermined validity duration of said temporary validation telephone number, - the verification of the correspondence between the temporary validation telephone number called and the validation procedure, to ensure that the communication terminal of the user emitted the call intended for the temporary validation telephone number, during the predetermined validity duration of said temporary validation telephone number, and - the validation of the telephone line of the user insofar as the correspondence between the temporary validation telephone number called by the communication terminal of the user and the validation procedure has been verified in the preceding step, such that the client system is able to authorise the user to use the service or software application.