You would need a GSM phone, not just a speaker. Your phone's radio can interfere with electronics like land-line phones. My Nexus 5, on a GSM/LTE network, will cause my Polycom speakerphone to make "dit-dit-dit" noises occasionally (when the network interrogates devices in range) if it is with a few inches of the speakerphone. I suspect people who think they can sense a call coming in are hearing the network looking for their phone in order to offer a call, and not sensing radio waves.