A method of proximity discovery between a first mobile communication device and a second mobile communication device for enabling the first mobile communication device and the second mobile communication device to set up a device-to-device communication session, wherein: the first mobile communication device is communicatively connected to a first communication network for receiving a first communication service via the first communication network in a first geographic area and in a first frequency-band; the second mobile communication device is communicatively connected to a second communication network, different from the first communication network, for receiving a second communication service via the second communication network in a second geographic area and in a second frequency-band; the first mobile communication device is configured for transmitting first information in a third frequency-band, disjoint from the first frequency-band and disjoint from the second frequency-band; the first information is representative of a first identifier of the first mobile communication device and of a first geographic location of the first mobile communication device; the second communication network is configured for monitoring the third frequency-band, the method comprising: receiving in the second communication network the first information from the first mobile communication device; under control of the first identifier consulting a database from the second communication network or second mobile communication device for determining if the first mobile communication device is listed as associated with the second mobile communication device; if the first mobile communication device is listed as associated with the second mobile communication device, determining a second geographic location of the second mobile communication device; and determining a spatial proximity between the first mobile communication device and the second mobile communication device based on the first geographic location and the second geographic location. the first mobile communication device is communicatively connected to a first communication network for receiving a first communication service via the first communication network in a first geographic area and in a first frequency-band; the second mobile communication device is communicatively connected to a second communication network, different from the first communication network, for receiving a second communication service via the second communication network in a second geographic area and in a second frequency-band; the first mobile communication device is configured for transmitting first information in a third frequency-band, disjoint from the first frequency-band and disjoint from the second frequency-band; the first information is representative of a first identifier of the first mobile communication device and of a first geographic location of the first mobile communication device; the second communication network is configured for monitoring the third frequency-band, the method comprising: receiving in the second communication network the first information from the first mobile communication device; under control of the first identifier consulting a database from the second communication network or second mobile communication device for determining if the first mobile communication device is listed as associated with the second mobile communication device; if the first mobile communication device is listed as associated with the second mobile communication device, determining a second geographic location of the second mobile communication device; and determining a spatial proximity between the first mobile communication device and the second mobile communication device based on the first geographic location and the second geographic location. receiving in the second communication network the first information from the first mobile communication device; under control of the first identifier consulting a database from the second communication network or second mobile communication device for determining if the first mobile communication device is listed as associated with the second mobile communication device; if the first mobile communication device is listed as associated with the second mobile communication device, determining a second geographic location of the second mobile communication device; and determining a spatial proximity between the first mobile communication device and the second mobile communication device based on the first geographic location and the second geographic location.