A method for preserving confidentiality of telephone numbers used in telemarketing campaigns, the method being implemented by a distributed system comprising: an originator, holding lists of unencrypted telephone numbers; a plurality of targets, each identified by its own telephone number; at least one call emitter forming at least one subcontractor, capable of establishing communication with each of the targets on the target list at the request of the originator; and a platform forming a trusted third party, in operational communication with the originator, the at least one subcontractor, and the targets, wherein the method comprises the implementation of a protocol for preserving confidentiality of the unencrypted telephone numbers towards the at least one subcontractor, comprising the following successive steps: in a preliminary step: a) by the originator, sending to the trusted third party an unencrypted message containing at least: authorized subcontractor(s) identifying data, and a set of telephone numbers (); b) by the trusted third party, encrypting the unencrypted message, to provide an encrypted message (F*) containing encrypted versions (STA*, {N*}) of the authorized subcontractor(s) identifying data and the telephone numbers; and c) by the trusted third party, sending the encrypted message (F*) to the originator; in a subsequent step: d) by the originator, sending the encrypted message (F*) to the at least one subcontractor; e) by the at least one subcontractor, sending the encrypted message (F*) with an encrypted telephone number (N*) to the trusted third party; f) by the trusted third party: decrypting and extracting of the authorized subcontractor(s) identifying data; checking that the message received at step d) comes from an authorized subcontractor; continuing the procedure in case of successful checking; and abandoning the procedure in the opposite case; h) by the trusted third party, decrypting and extracting the encrypted telephone number (N*); i) by the trusted third party, establishing a telephone connection (30, 32, 34) of the at least one subcontractor with the target from the telephone number decrypted at step h), without transmitting the decrypted telephone number to the at least one subcontractor. an originator, holding lists of unencrypted telephone numbers; a plurality of targets, each identified by its own telephone number; at least one call emitter forming at least one subcontractor, capable of establishing communication with each of the targets on the target list at the request of the originator; and a platform forming a trusted third party, in operational communication with the originator, the at least one subcontractor, and the targets, in a preliminary step: a) by the originator, sending to the trusted third party an unencrypted message containing at least: authorized subcontractor(s) identifying data, and a set of telephone numbers (); b) by the trusted third party, encrypting the unencrypted message, to provide an encrypted message (F*) containing encrypted versions (STA*, {N*}) of the authorized subcontractor(s) identifying data and the telephone numbers; and c) by the trusted third party, sending the encrypted message (F*) to the originator; a) by the originator, sending to the trusted third party an unencrypted message containing at least: authorized subcontractor(s) identifying data, and a set of telephone numbers (); b) by the trusted third party, encrypting the unencrypted message, to provide an encrypted message (F*) containing encrypted versions (STA*, {N*}) of the authorized subcontractor(s) identifying data and the telephone numbers; and c) by the trusted third party, sending the encrypted message (F*) to the originator; in a subsequent step: d) by the originator, sending the encrypted message (F*) to the at least one subcontractor; e) by the at least one subcontractor, sending the encrypted message (F*) with an encrypted telephone number (N*) to the trusted third party; f) by the trusted third party: decrypting and extracting of the authorized subcontractor(s) identifying data; checking that the message received at step d) comes from an authorized subcontractor; continuing the procedure in case of successful checking; and abandoning the procedure in the opposite case; h) by the trusted third party, decrypting and extracting the encrypted telephone number (N*); i) by the trusted third party, establishing a telephone connection (30, 32, 34) of the at least one subcontractor with the target from the telephone number decrypted at step h), without transmitting the decrypted telephone number to the at least one subcontractor. d) by the originator, sending the encrypted message (F*) to the at least one subcontractor; e) by the at least one subcontractor, sending the encrypted message (F*) with an encrypted telephone number (N*) to the trusted third party; f) by the trusted third party: decrypting and extracting of the authorized subcontractor(s) identifying data; checking that the message received at step d) comes from an authorized subcontractor; continuing the procedure in case of successful checking; and abandoning the procedure in the opposite case; h) by the trusted third party, decrypting and extracting the encrypted telephone number (N*); i) by the trusted third party, establishing a telephone connection (30, 32, 34) of the at least one subcontractor with the target from the telephone number decrypted at step h), without transmitting the decrypted telephone number to the at least one subcontractor.