If the hearing aid with the touchless t-coil was prescribed to provide sufficient amplification according to your hearing loss, the signal should be as strong as the signal from your BTE. The only difference should be the activation of the Telephone mode. Most hearing aid manufacturers observe guidelines when manufacturing telephone compatibility to ensure the strength of the signals are compatible with each hearing loss. The key, therefore, resides in the strength of the signal and is related directly to the power and the gain of the hearing aid. The power and the gain of the hearing aid relates to the degree of the hearing loss, so if an adequate gain is prescribed, the telecoil signal should be sufficiently loud to hear on the telephone regardless of the engaging system. The interference, on the other hand, should be the same as the interference perceived with the regular t-coil from a BTE. If the aids are closer than two feet to the source, then interference will be perceived as a humming sound.