core/homeassistant/components/modem_callerid/icons.json

{
  "entity": {
    "button": {
      "phone_modem_reject": {
        "default": "mdi:phone-hangup"
      }
    },
    "sensor": {
      "incoming_call": {
        "default": "mdi:phone-classic"
      }
    }
  }
}