The Wifi, GPS, and Bluetooth antennas can be replaced and work again. However, if you are having problems with phone calls- a new cellular antenna will NOT fix the problem. Typically the motherboard is the culprit. Dropping calls and Searching problems can sometimes be fixed, but not because of a new antenna. A flaky cellular antenna can be eliminated as a source of the problem by running a speed test in a great signal area for your cell phone provider. In very rare cases, the battery or a silly software hiccup can cause the phone to say Searching.
iPhone 6 WiFi or GPS Antenna - $65